diff --git a/frontend/src/components/AnalysisCharts.jsx b/frontend/src/components/AnalysisCharts.jsx
index c1a2738..536da13 100644
--- a/frontend/src/components/AnalysisCharts.jsx
+++ b/frontend/src/components/AnalysisCharts.jsx
@@ -4,6 +4,8 @@ import {
   LineChart, Line, XAxis, YAxis, CartesianGrid, Tooltip,
   Legend, ResponsiveContainer,
 } from 'recharts';
+import { SubjectSidebar } from './SubjectSidebar';
+import { sortPayloadByValueDesc, toggleInSet, setIdsHidden } from '../lib/crossSubjectChart';
 
 // ── Color palettes ─────────────────────────────────────────────────────────────
 
@@ -453,6 +455,15 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
   const [xField,   setXField]   = useState(() => defaultXField(xAxisFields));
   const [tickStep, setTickStep] = useState(1);
 
+  // Cross-subject interaction state (client-only; global across both charts)
+  const [sidebarOpen,        setSidebarOpen]        = useState(false);
+  const [hiddenSubjects,     setHiddenSubjects]     = useState(() => new Set());
+  const [highlightedSubject, setHighlightedSubject] = useState(null);
+
+  const toggleHidden = (id)          => setHiddenSubjects((prev) => toggleInSet(prev, id));
+  const toggleGroup  = (ids, hidden) => setHiddenSubjects((prev) => setIdsHidden(prev, ids, hidden));
+  const showAll      = ()            => setHiddenSubjects(new Set());
+
   const countsS = useChartSettings(200);
   const rateS   = useChartSettings(160);
 
@@ -517,16 +528,17 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
 
   function ExpTooltip({ active, payload, label, unit = '' }) {
     if (!active || !payload?.length) return null;
+    const rows = sortPayloadByValueDesc(payload);
     return (
       <div className="bg-white border border-gray-200 rounded shadow-sm px-3 py-2 text-xs space-y-0.5 max-h-48 overflow-y-auto">
         <p className="font-semibold text-gray-700 mb-1">{label}</p>
-        {payload.map((p) => {
+        {rows.map((p) => {
           const line = lines.find((l) => l.id === p.dataKey);
-          return p.value != null ? (
+          return (
             <p key={p.dataKey} style={{ color: p.stroke }}>
               {line?.name ?? p.dataKey}{line?.group && line.group !== '—' ? ` (${line.group})` : ''}: {p.value}{unit}
             </p>
-          ) : null;
+          );
         })}
       </div>
     );
@@ -554,6 +566,17 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
           </div>
         )}
         <TickStepControl value={tickStep} onChange={setTickStep} />
+        {hasData && (
+          <button type="button" onClick={() => setSidebarOpen((o) => !o)}
+            className={[
+              'text-xs px-2 py-0.5 rounded border transition-colors ml-auto',
+              sidebarOpen
+                ? 'bg-gray-100 border-gray-300 text-gray-700'
+                : 'bg-white border-gray-200 text-gray-500 hover:text-gray-700 hover:border-gray-300',
+            ].join(' ')}>
+            {sidebarOpen ? '◂ Subjects' : '▸ Subjects'}
+          </button>
+        )}
       </div>
 
       {!hasData && (
@@ -561,7 +584,8 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
       )}
 
       {hasData && (
-        <>
+        <div className="flex gap-3 items-start">
+          <div className="flex-1 min-w-0 space-y-5">
           {/* Chart 1 — counts */}
           <div>
             <div className="flex items-center justify-between mb-2 flex-wrap gap-2">
@@ -600,10 +624,16 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
                 <YAxis tick={{ fontSize: 10 }} width={30} allowDecimals={false} domain={countsS.yDomain} />
                 <Tooltip content={<ExpTooltip />} />
                 <Legend wrapperStyle={{ fontSize: 11 }}
-                  formatter={(value) => lines.find((l) => l.id === value)?.name ?? value} />
+                  formatter={(value) => lines.find((l) => l.id === value)?.name ?? value}
+                  onClick={(o) => toggleHidden(o.dataKey)}
+                  onMouseEnter={(o) => setHighlightedSubject(o.dataKey)}
+                  onMouseLeave={() => setHighlightedSubject(null)} />
                 {lines.map((l) => (
                   <Line key={l.id} type="monotone" dataKey={l.id} name={l.id}
-                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }}
+                    stroke={l.color}
+                    strokeWidth={highlightedSubject === l.id ? 3.5 : 2}
+                    hide={hiddenSubjects.has(l.id)}
+                    dot={{ r: 3 }} activeDot={{ r: 5 }}
                     connectNulls isAnimationActive={false} />
                 ))}
               </LineChart>
@@ -625,16 +655,33 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
                   tickFormatter={(v) => `${v}%`} />
                 <Tooltip content={<ExpTooltip unit="%" />} />
                 <Legend wrapperStyle={{ fontSize: 11 }}
-                  formatter={(value) => lines.find((l) => l.id === value)?.name ?? value} />
+                  formatter={(value) => lines.find((l) => l.id === value)?.name ?? value}
+                  onClick={(o) => toggleHidden(o.dataKey)}
+                  onMouseEnter={(o) => setHighlightedSubject(o.dataKey)}
+                  onMouseLeave={() => setHighlightedSubject(null)} />
                 {lines.map((l) => (
                   <Line key={l.id} type="monotone" dataKey={l.id} name={l.id}
-                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }}
+                    stroke={l.color}
+                    strokeWidth={highlightedSubject === l.id ? 3.5 : 2}
+                    hide={hiddenSubjects.has(l.id)}
+                    dot={{ r: 3 }} activeDot={{ r: 5 }}
                     connectNulls isAnimationActive={false} />
                 ))}
               </LineChart>
             </ResponsiveContainer>
           </div>
-        </>
+          </div>
+          {sidebarOpen && (
+            <SubjectSidebar
+              lines={lines}
+              hiddenSubjects={hiddenSubjects}
+              onToggleSubject={toggleHidden}
+              onToggleGroup={toggleGroup}
+              onShowAll={showAll}
+              onHighlight={setHighlightedSubject}
+            />
+          )}
+        </div>
       )}
     </div>
   );
diff --git a/frontend/tests/ExperimentAnalysisCharts.test.jsx b/frontend/tests/ExperimentAnalysisCharts.test.jsx
new file mode 100644
index 0000000..17c2021
--- /dev/null
+++ b/frontend/tests/ExperimentAnalysisCharts.test.jsx
@@ -0,0 +1,61 @@
+import React from 'react';
+import { render, screen, fireEvent } from '@testing-library/react';
+
+// recharts uses ResizeObserver (absent in jsdom); stub all used pieces as passthroughs.
+// Coverage boundary: with recharts mocked out, these tests cover only the sidebar
+// integration path (toggle, checkbox state, persistence). The legend onClick/hover
+// wiring, line hide/strokeWidth, and tooltip ordering are exercised by the pure-helper
+// unit tests (crossSubjectChart.test.js) and SubjectSidebar.test.jsx.
+jest.mock('recharts', () => {
+  const Pass = ({ children }) => <div>{children}</div>;
+  return {
+    ResponsiveContainer: Pass, LineChart: Pass, Line: () => null,
+    XAxis: () => null, YAxis: () => null, CartesianGrid: () => null,
+    Tooltip: () => null, Legend: () => null,
+  };
+});
+
+import { ExperimentAnalysisCharts } from '../src/components/AnalysisCharts';
+
+const ANIMALS = [
+  { id: 'a1', animal_name: 'Mouse-A1', subject_info: { grp: 'Group A' } },
+  { id: 'b1', animal_name: 'Mouse-B1', subject_info: { grp: 'Group B' } },
+];
+const STATUSES = [
+  { animal_id: 'a1', date: '2026-01-01', analysis_summary: { total: 10, success_rate: 0.5, counts: { Success: 5 } } },
+  { animal_id: 'b1', date: '2026-01-01', analysis_summary: { total: 8, success_rate: 0.25, counts: { Success: 2 } } },
+];
+const SUBJECT_TEMPLATE = [{ fieldId: 'grp', label: 'Group', active: true }];
+const DAILY_TEMPLATE = [];
+
+function renderChart() {
+  render(
+    <ExperimentAnalysisCharts
+      animals={ANIMALS}
+      experimentStatuses={STATUSES}
+      subjectTemplate={SUBJECT_TEMPLATE}
+      dailyTemplate={DAILY_TEMPLATE}
+    />,
+  );
+}
+
+it('toggles the subject sidebar open and closed', () => {
+  renderChart();
+  expect(screen.queryByText('Subjects')).toBeNull();
+  fireEvent.click(screen.getByText('▸ Subjects'));
+  expect(screen.getByText('Subjects')).toBeInTheDocument();
+  expect(screen.getByLabelText('Mouse-A1')).toBeInTheDocument();
+  expect(screen.getByLabelText('Mouse-B1')).toBeInTheDocument();
+  fireEvent.click(screen.getByText('◂ Subjects'));
+  expect(screen.queryByText('Subjects')).toBeNull();
+});
+
+it('unchecking a subject in the sidebar persists across re-render', () => {
+  renderChart();
+  fireEvent.click(screen.getByText('▸ Subjects'));
+  const cb = screen.getByLabelText('Mouse-A1');
+  expect(cb.checked).toBe(true);
+  fireEvent.click(cb);
+  expect(screen.getByLabelText('Mouse-A1').checked).toBe(false);
+  expect(screen.getByText('Show all')).toBeInTheDocument();
+});