diff --git a/js/app.js b/js/app.js
index a213979..673a56f 100644
--- a/js/app.js
+++ b/js/app.js
@@ -47,7 +47,7 @@ const opts = () => ({
   tongueReject: +el('tongueReject').value / 100,
   blobGrow: +el('blobGrow').value,
   topBias: +el('topBias').value / 100,
-  verts: +el('teethVerts').value,
+  teethVerts: +el('teethVerts').value,
   smoothWin: +el('smoothWin').value,
   contourSmooth: +el('contourSmooth').value,
   apertureThresh: +el('apertureThresh').value / 1000,
@@ -146,7 +146,7 @@ function measureAll(images, dense, o) {
 // Extraction keys on every knob that changes the pixels examined, so the cache
 // is keyed on exactly those and a change to anything else stays instant.
 const extractKey = (o) =>
-  [o.cavityErode, o.tongueReject, o.blobGrow, o.topBias, o.verts].join('|');
+  [o.cavityErode, o.tongueReject, o.blobGrow, o.topBias, o.teethVerts].join('|');
 
 /* ---------- build ---------- */
 
diff --git a/js/interior.js b/js/interior.js
index f3d7053..226475a 100644
--- a/js/interior.js
+++ b/js/interior.js
@@ -191,7 +191,7 @@ export function extractTeeth(img, innerNorm, ctx, o, wantDebug = false) {
   for (const i of comp.px) { only[i] = 1; cx += i % pw; cy += (i / pw) | 0; }
   cx /= comp.px.length; cy /= comp.px.length;
 
-  const local = radialContour(only, pw, ph, cx, cy, o.verts ?? 10);
+  const local = radialContour(only, pw, ph, cx, cy, o.teethVerts ?? 10);
   const contour = local.map((p) => ({ x: (p.x + px0) / W, y: (p.y + py0) / H }));
 
   return {
diff --git a/js/selftest.js b/js/selftest.js
index 24cae67..82abc7f 100644
--- a/js/selftest.js
+++ b/js/selftest.js
@@ -63,6 +63,19 @@ export async function runWiring() {
     if (list) {
       for (const m of list[1].matchAll(/'([\w]+)'/g)) { ids.add(m[1]); ids.add(m[1] + 'v'); }
     }
+    // Duplicate keys in an object literal are silent in JS - the last one wins.
+    // In opts() that meant the teeth vertex slider was quietly driving the lip
+    // vertex count while the lip slider did nothing at all.
+    const lit = app.match(/const opts = \(\) => \(\{([\s\S]*?)\n\}\);/);
+    if (lit) {
+      const keys = [...lit[1].matchAll(/^\s*([A-Za-z_$][\w$]*)\s*:/gm)].map((m) => m[1]);
+      const dupes = keys.filter((k, i) => keys.indexOf(k) !== i);
+      out.push({ name: `opts() has no duplicate keys (${keys.length} checked)`,
+                 pass: dupes.length === 0, detail: [...new Set(dupes)].join(', ') });
+    } else {
+      out.push({ name: 'opts() literal found for duplicate-key check', pass: false, detail: '' });
+    }
+
     const have = new Set([...html.matchAll(/id="([\w-]+)"/g)].map((m) => m[1]));
     const missing = [...ids].filter((i) => !have.has(i));
     out.push({ name: `every el() id exists in index.html (${ids.size} checked)`,