diff --git a/src/animaltrack/web/routes/events.py b/src/animaltrack/web/routes/events.py
index 23df35f..c49031f 100644
--- a/src/animaltrack/web/routes/events.py
+++ b/src/animaltrack/web/routes/events.py
@@ -247,29 +247,60 @@ def event_log_index(request: Request, htmx):
     )
 
 
-def get_event_animals(db: Any, event_id: str) -> list[dict[str, Any]]:
+def get_event_animals(db: Any, event_id: str, limit: int | None = None) -> list[dict[str, Any]]:
     """Get animals affected by an event with display info.
 
     Args:
         db: Database connection.
         event_id: Event ID to look up animals for.
+        limit: Maximum number of animals to return (None for all).
 
     Returns:
-        List of animal dicts with id, nickname, species_name.
+        List of animal dicts with id, nickname, species_name, sex, life_stage, location_name.
     """
-    rows = db.execute(
-        """
-        SELECT ar.animal_id, ar.nickname, s.name as species_name
+    query = """
+        SELECT ar.animal_id, ar.nickname, s.name as species_name,
+               ar.sex, ar.life_stage, l.name as location_name
         FROM event_animals ea
         JOIN animal_registry ar ON ar.animal_id = ea.animal_id
         JOIN species s ON s.code = ar.species_code
+        LEFT JOIN locations l ON l.id = ar.location_id
         WHERE ea.event_id = ?
         ORDER BY ar.nickname NULLS LAST, ar.animal_id
-        """,
-        (event_id,),
-    ).fetchall()
+    """
+    if limit:
+        query += f" LIMIT {limit}"
 
-    return [{"id": row[0], "nickname": row[1], "species_name": row[2]} for row in rows]
+    rows = db.execute(query, (event_id,)).fetchall()
+
+    return [
+        {
+            "id": row[0],
+            "nickname": row[1],
+            "species_name": row[2],
+            "sex": row[3],
+            "life_stage": row[4],
+            "location_name": row[5],
+        }
+        for row in rows
+    ]
+
+
+def get_event_animal_count(db: Any, event_id: str) -> int:
+    """Get count of animals affected by an event.
+
+    Args:
+        db: Database connection.
+        event_id: Event ID to count animals for.
+
+    Returns:
+        Total number of animals affected.
+    """
+    row = db.execute(
+        "SELECT COUNT(*) FROM event_animals WHERE event_id = ?",
+        (event_id,),
+    ).fetchone()
+    return row[0] if row else 0
 
 
 @ar("/events/{event_id}")
@@ -292,8 +323,9 @@ def event_detail(request: Request, event_id: str, htmx):
     # Check if tombstoned
     is_tombstoned = event_store.is_tombstoned(event_id)
 
-    # Get affected animals
-    affected_animals = get_event_animals(db, event_id)
+    # Get affected animals (limited to first 20 for performance)
+    affected_animals = get_event_animals(db, event_id, limit=20)
+    total_animal_count = get_event_animal_count(db, event_id)
 
     # Get location names if entity_refs has location IDs
     location_names = {}
@@ -317,7 +349,9 @@ def event_detail(request: Request, event_id: str, htmx):
     user_role = auth.role if auth else None
 
     # Build the panel
-    panel = event_detail_panel(event, affected_animals, is_tombstoned, location_names, user_role)
+    panel = event_detail_panel(
+        event, affected_animals, total_animal_count, is_tombstoned, location_names, user_role
+    )
 
     # HTMX request (slide-over) → return just panel
     if htmx.request:
@@ -327,6 +361,24 @@ def event_detail(request: Request, event_id: str, htmx):
     return render_page(request, panel, title=f"Event {event.id}")
 
 
+@ar("/events/{event_id}/animals")
+def event_animals_all(request: Request, event_id: str):
+    """GET /events/{event_id}/animals - Get all affected animals for an event.
+
+    This endpoint is used via HTMX to load the full list when user clicks "Show all".
+    """
+    from animaltrack.web.templates.event_detail import affected_animals_list
+
+    db = request.app.state.db
+
+    # Get all animals (no limit)
+    animals = get_event_animals(db, event_id)
+    total_count = len(animals)
+
+    # Return just the list component for HTMX swap
+    return affected_animals_list(animals, total_count, expanded=True)
+
+
 @ar("/events/{event_id}/delete", methods=["POST"])
 async def event_delete(request: Request, event_id: str):
     """POST /events/{event_id}/delete - Delete an event (admin only).
diff --git a/src/animaltrack/web/templates/event_detail.py b/src/animaltrack/web/templates/event_detail.py
index 5ebe28a..1880b02 100644
--- a/src/animaltrack/web/templates/event_detail.py
+++ b/src/animaltrack/web/templates/event_detail.py
@@ -20,6 +20,7 @@ def format_timestamp(ts_utc: int) -> str:
 def event_detail_panel(
     event: Event,
     affected_animals: list[dict[str, Any]],
+    total_animal_count: int = 0,
     is_tombstoned: bool = False,
     location_names: dict[str, str] | None = None,
     user_role: UserRole | None = None,
@@ -28,7 +29,8 @@ def event_detail_panel(
 
     Args:
         event: The event to display.
-        affected_animals: List of animals affected by this event.
+        affected_animals: List of animals affected by this event (may be limited).
+        total_animal_count: Total number of affected animals.
         is_tombstoned: Whether the event has been deleted.
         location_names: Map of location IDs to names.
         user_role: User's role for delete button visibility.
@@ -38,6 +40,8 @@ def event_detail_panel(
     """
     if location_names is None:
         location_names = {}
+    if total_animal_count == 0:
+        total_animal_count = len(affected_animals)
 
     return Div(
         # Header with close button
@@ -69,7 +73,7 @@ def event_detail_panel(
         # Entity references
         entity_refs_section(event.entity_refs, location_names),
         # Affected animals
-        affected_animals_section(affected_animals),
+        affected_animals_section(affected_animals, total_animal_count, event.id),
         # Delete button (admin only, not for tombstoned events)
         delete_section(event.id) if user_role == UserRole.ADMIN and not is_tombstoned else None,
         id="event-panel-content",
@@ -355,20 +359,76 @@ def entity_refs_section(
     )
 
 
-def affected_animals_section(animals: list[dict[str, Any]]) -> Div:
-    """Section showing affected animals."""
-    if not animals:
+def affected_animals_section(
+    animals: list[dict[str, Any]],
+    total_count: int,
+    event_id: str,
+) -> Div:
+    """Section showing affected animals with expandable list.
+
+    Args:
+        animals: List of animals to display (may be limited).
+        total_count: Total number of affected animals.
+        event_id: Event ID for "Show all" button.
+
+    Returns:
+        Div containing the affected animals section.
+    """
+    if not animals and total_count == 0:
         return Div()
 
+    return Div(
+        H3(
+            f"Affected Animals ({total_count})",
+            cls="text-sm font-semibold text-stone-400 mb-2",
+        ),
+        affected_animals_list(animals, total_count, event_id=event_id),
+        cls="p-4",
+        id="affected-animals-section",
+    )
+
+
+def affected_animals_list(
+    animals: list[dict[str, Any]],
+    total_count: int,
+    event_id: str | None = None,
+    expanded: bool = False,
+) -> Div:
+    """List of affected animals with optional expand button.
+
+    Args:
+        animals: List of animals to display.
+        total_count: Total number of affected animals.
+        event_id: Event ID for "Show all" button (None if expanded).
+        expanded: Whether showing full list.
+
+    Returns:
+        Div containing the animal list.
+    """
     animal_items = []
-    for animal in animals[:20]:  # Limit display
+    for animal in animals:
         display_name = format_animal_id(animal["id"], animal.get("nickname"))
+
+        # Build details string: sex abbreviation, life stage, location
+        sex_abbr = {"male": "M", "female": "F", "unknown": "?"}.get(
+            animal.get("sex", "unknown"), "?"
+        )
+        life_stage = animal.get("life_stage", "").replace("_", " ")
+        location = animal.get("location_name", "")
+
+        details_parts = [sex_abbr]
+        if life_stage:
+            details_parts.append(life_stage)
+        if location:
+            details_parts.append(location)
+        details_str = ", ".join(details_parts)
+
         animal_items.append(
             Li(
                 A(
-                    Span(display_name, cls="text-amber-500 hover:underline"),
+                    Span(display_name, cls="text-amber-500 hover:underline mr-1"),
                     Span(
-                        f" ({animal.get('species_name', '')})",
+                        f"({details_str})",
                         cls="text-stone-500 text-xs",
                     ),
                     href=f"/animals/{animal['id']}",
@@ -377,22 +437,23 @@ def affected_animals_section(animals: list[dict[str, Any]]) -> Div:
             )
         )
 
-    more_count = len(animals) - 20
-    if more_count > 0:
-        animal_items.append(
-            Li(
-                Span(f"... and {more_count} more", cls="text-stone-500 text-sm"),
-                cls="py-1",
-            )
+    # Show "Show all X animals" button if there are more
+    more_count = total_count - len(animals)
+    show_all_button = None
+    if more_count > 0 and not expanded and event_id:
+        show_all_button = Button(
+            f"Show all {total_count} animals",
+            hx_get=f"/events/{event_id}/animals",
+            hx_target="#affected-animals-list",
+            hx_swap="outerHTML",
+            cls="mt-2 text-sm text-amber-500 hover:text-amber-400 hover:underline",
+            type="button",
         )
 
     return Div(
-        H3(
-            f"Affected Animals ({len(animals)})",
-            cls="text-sm font-semibold text-stone-400 mb-2",
-        ),
         Ul(*animal_items, cls="space-y-1"),
-        cls="p-4",
+        show_all_button,
+        id="affected-animals-list",
     )
 
 
diff --git a/src/animaltrack/web/templates/registry.py b/src/animaltrack/web/templates/registry.py
index a33244a..2c15d1e 100644
--- a/src/animaltrack/web/templates/registry.py
+++ b/src/animaltrack/web/templates/registry.py
@@ -5,7 +5,24 @@ from datetime import UTC, datetime
 from typing import Any
 from urllib.parse import urlencode
 
-from fasthtml.common import H2, A, Div, Form, Input, P, Span, Table, Tbody, Td, Th, Thead, Tr
+from fasthtml.common import (
+    H2,
+    A,
+    Div,
+    Form,
+    Input,
+    Li,
+    P,
+    Script,
+    Span,
+    Table,
+    Tbody,
+    Td,
+    Th,
+    Thead,
+    Tr,
+    Ul,
+)
 from monsterui.all import Button, ButtonT, FormLabel, Grid
 
 from animaltrack.id_gen import format_animal_id
@@ -43,9 +60,11 @@ def registry_page(
         Grid(
             # Sidebar with facets
             facet_sidebar(facets, filter_str, locations, species_list),
-            # Main content - table
+            # Main content - selection toolbar + table
             Div(
+                selection_toolbar(),
                 animal_table(animals, next_cursor, filter_str),
+                selection_script(),
                 cls="col-span-3",
             ),
             cols_sm=1,
@@ -203,6 +222,14 @@ def animal_table(
     return Table(
         Thead(
             Tr(
+                Th(
+                    Input(
+                        type="checkbox",
+                        id="select-all-checkbox",
+                        cls="uk-checkbox",
+                    ),
+                    cls="w-8",
+                ),
                 Th("ID", shrink=True),
                 Th("Species"),
                 Th("Sex"),
@@ -254,6 +281,13 @@ def animal_row(animal: AnimalListItem) -> Tr:
         tags_str += "..."
 
     return Tr(
+        Td(
+            Input(
+                type="checkbox",
+                cls="uk-checkbox animal-checkbox",
+                data_animal_id=animal.animal_id,
+            ),
+        ),
         Td(
             A(
                 display_id,
@@ -319,10 +353,208 @@ def load_more_sentinel(cursor: str, filter_str: str) -> Tr:
                 "Loading more...",
                 cls="text-center text-stone-400 py-4",
             ),
-            colspan="8",
+            colspan="9",  # Updated for checkbox column
         ),
         hx_get=url,
         hx_trigger="revealed",
         hx_swap="outerHTML",
         id="load-more-sentinel",
     )
+
+
+def selection_toolbar() -> Div:
+    """Toolbar for bulk actions on selected animals.
+
+    Returns:
+        Div with selection count and actions dropdown.
+    """
+    return Div(
+        # Left side: selection info and controls
+        Div(
+            Span("0 selected", id="selection-count", cls="text-sm text-stone-400"),
+            A(
+                "Select all",
+                href="#",
+                id="select-all-btn",
+                cls="text-sm text-amber-500 hover:underline ml-3",
+            ),
+            A(
+                "Clear",
+                href="#",
+                id="clear-selection-btn",
+                cls="text-sm text-stone-400 hover:text-stone-200 ml-3 hidden",
+            ),
+            cls="flex items-center",
+        ),
+        # Right side: actions dropdown
+        Div(
+            Button(
+                "Actions",
+                id="actions-btn",
+                cls=f"{ButtonT.default} px-4",
+                disabled=True,
+            ),
+            Div(
+                Ul(
+                    Li(
+                        A(
+                            "Move",
+                            href="#",
+                            data_action="move",
+                            cls="block px-4 py-2 hover:bg-stone-700",
+                        )
+                    ),
+                    Li(
+                        A(
+                            "Add Tag",
+                            href="#",
+                            data_action="tag-add",
+                            cls="block px-4 py-2 hover:bg-stone-700",
+                        )
+                    ),
+                    Li(
+                        A(
+                            "Update Attributes",
+                            href="#",
+                            data_action="attrs",
+                            cls="block px-4 py-2 hover:bg-stone-700",
+                        )
+                    ),
+                    Li(
+                        A(
+                            "Record Outcome",
+                            href="#",
+                            data_action="outcome",
+                            cls="block px-4 py-2 hover:bg-stone-700",
+                        )
+                    ),
+                    cls="uk-nav uk-dropdown-nav",
+                ),
+                uk_dropdown="mode: click; pos: bottom-right",
+                cls="uk-dropdown",
+            ),
+            cls="uk-inline",
+        ),
+        cls="flex justify-between items-center mb-4 py-2 px-3 bg-stone-800/50 rounded",
+        id="selection-toolbar",
+    )
+
+
+def selection_script() -> Script:
+    """JavaScript for handling animal selection.
+
+    Returns:
+        Script element with selection logic.
+    """
+    return Script("""
+    (function() {
+        const selectedIds = new Set();
+
+        function updateUI() {
+            const count = selectedIds.size;
+            document.getElementById('selection-count').textContent = count + ' selected';
+
+            const actionsBtn = document.getElementById('actions-btn');
+            actionsBtn.disabled = count === 0;
+
+            const clearBtn = document.getElementById('clear-selection-btn');
+            if (count > 0) {
+                clearBtn.classList.remove('hidden');
+            } else {
+                clearBtn.classList.add('hidden');
+            }
+
+            // Update all checkboxes to reflect state
+            document.querySelectorAll('.animal-checkbox').forEach(cb => {
+                cb.checked = selectedIds.has(cb.dataset.animalId);
+            });
+
+            // Update header checkbox
+            const headerCb = document.getElementById('select-all-checkbox');
+            const allCheckboxes = document.querySelectorAll('.animal-checkbox');
+            if (allCheckboxes.length > 0) {
+                const allChecked = Array.from(allCheckboxes).every(cb => selectedIds.has(cb.dataset.animalId));
+                const someChecked = selectedIds.size > 0;
+                headerCb.checked = allChecked;
+                headerCb.indeterminate = someChecked && !allChecked;
+            }
+        }
+
+        // Handle individual checkbox changes
+        document.addEventListener('change', function(e) {
+            if (e.target.classList.contains('animal-checkbox')) {
+                const animalId = e.target.dataset.animalId;
+                if (e.target.checked) {
+                    selectedIds.add(animalId);
+                } else {
+                    selectedIds.delete(animalId);
+                }
+                updateUI();
+            }
+        });
+
+        // Handle header checkbox (select all visible)
+        document.getElementById('select-all-checkbox').addEventListener('change', function(e) {
+            document.querySelectorAll('.animal-checkbox').forEach(cb => {
+                if (e.target.checked) {
+                    selectedIds.add(cb.dataset.animalId);
+                } else {
+                    selectedIds.delete(cb.dataset.animalId);
+                }
+            });
+            updateUI();
+        });
+
+        // Select all button
+        document.getElementById('select-all-btn').addEventListener('click', function(e) {
+            e.preventDefault();
+            document.querySelectorAll('.animal-checkbox').forEach(cb => {
+                selectedIds.add(cb.dataset.animalId);
+            });
+            updateUI();
+        });
+
+        // Clear selection button
+        document.getElementById('clear-selection-btn').addEventListener('click', function(e) {
+            e.preventDefault();
+            selectedIds.clear();
+            updateUI();
+        });
+
+        // Handle action clicks
+        document.querySelectorAll('[data-action]').forEach(link => {
+            link.addEventListener('click', function(e) {
+                e.preventDefault();
+                if (selectedIds.size === 0) return;
+
+                const action = this.dataset.action;
+                const filter = 'animal_id:' + Array.from(selectedIds).join('|');
+
+                let url;
+                switch(action) {
+                    case 'move':
+                        url = '/move?filter=' + encodeURIComponent(filter);
+                        break;
+                    case 'tag-add':
+                        url = '/actions/tag-add?filter=' + encodeURIComponent(filter);
+                        break;
+                    case 'attrs':
+                        url = '/actions/attrs?filter=' + encodeURIComponent(filter);
+                        break;
+                    case 'outcome':
+                        url = '/actions/outcome?filter=' + encodeURIComponent(filter);
+                        break;
+                }
+                if (url) {
+                    window.location.href = url;
+                }
+            });
+        });
+
+        // Re-run updateUI after HTMX swaps (for infinite scroll)
+        document.body.addEventListener('htmx:afterSwap', function(e) {
+            // After new rows are loaded, restore checkbox states
+            updateUI();
+        });
+    })();
+    """)