diff --git a/docs/09-ART-PIPELINE.md b/docs/09-ART-PIPELINE.md
index 7b49693..170a65d 100644
--- a/docs/09-ART-PIPELINE.md
+++ b/docs/09-ART-PIPELINE.md
@@ -280,6 +280,7 @@ The team's open question in A14: how do generated frames move without looking li
 4. **Smears instead of blends** for fast motion: one stretched smear frame on the chair swing and the knockback, as in Spider-Verse. No motion blur or warp.
 5. **One grid, one palette.** Everything is crushed to the same pixel scale and 96-colour palette, and the feet are anchored to one baseline row, so frames don't wobble.
 6. **Preview before approval.** Every sheet gets a looping preview at game size on its review page. A frame that pops is redrawn on its own against its neighbours as inputs.
+7. **Check the switches in motion.** `python scripts/transition_gifs.py` runs the game's own movement, jump and animation code (`game/verification/transitions/trace.ts`) through idle ↔ walk ↔ run ↔ jump ↔ land and draws each transition as a GIF at 30 fps, with ground ticks every foot that move with the world. A foot that slides against the ticks slides in the game; a clip switch should move the outline no more than the cycle's own frame-to-frame step.
 
 ## The crossing (no animation budget)
 
diff --git a/game/verification/transitions/idle-jump-land.gif b/game/verification/transitions/idle-jump-land.gif
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index 0000000..bdd11b1
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diff --git a/game/verification/transitions/idle-run-idle.gif b/game/verification/transitions/idle-run-idle.gif
new file mode 100644
index 0000000..b121768
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diff --git a/game/verification/transitions/idle-walk-idle.gif b/game/verification/transitions/idle-walk-idle.gif
new file mode 100644
index 0000000..dc9aa58
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diff --git a/game/verification/transitions/run-jump-land-run.gif b/game/verification/transitions/run-jump-land-run.gif
new file mode 100644
index 0000000..19c60c7
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diff --git a/game/verification/transitions/trace.ts b/game/verification/transitions/trace.ts
new file mode 100644
index 0000000..4e70dab
--- /dev/null
+++ b/game/verification/transitions/trace.ts
@@ -0,0 +1,64 @@
+/**
+ * The hero's locomotion transitions (#156 "Smooth transitions"), traced with the game's own code: movement.ts
+ * paces the body, jump.ts its arc and landing, animation.ts picks the frame – as player.ts wires them, on flat
+ * ground at the game's 120 Hz step. Writes one trace per transition; scripts/transition_gifs.py draws them.
+ *
+ *   node --experimental-transform-types game/verification/transitions/trace.ts > tmp/transitions.json
+ */
+import { readFileSync } from 'node:fs';
+import { catalogue, clipLength, LocomotionAnimation, type MotionPose } from '../../src/player/animation.ts';
+import { move, movement, RUN_SPEED, WALK_SPEED } from '../../src/player/movement.ts';
+import { GRAVITY, JUMP_SPEED, jumpState, landing, LANDING_TIMES } from '../../src/player/jump.ts';
+import type { AnimationTable } from '../../src/stage/assets.ts';
+
+const SPRITES = new URL('../../public/assets/sprites/', import.meta.url);
+const BOARDS = ['hero-move', 'hero-run', 'hero-air', 'hero-idle'];
+const tables = Object.fromEntries(BOARDS.map(board =>
+  [board, JSON.parse(readFileSync(new URL(`${board}.anims.json`, SPRITES), 'utf8')) as AnimationTable]));
+const clips = catalogue(tables);
+// The landing holds, as player.ts measures them from the jump row's landing and the hard landing.
+const times = clips.land && clips['hard-landing']
+  ? { soft: clipLength(clips.land, 'land'), hard: clipLength(clips['hard-landing'], 'hard-landing') } : LANDING_TIMES;
+
+/** One input phase: hold right (axis), and/or press jump at its start, for `seconds`. */
+type Phase = { seconds: number; axis: number; jump?: boolean };
+const SCRIPTS: Record<string, Phase[]> = {
+  'idle-walk-idle': [{ seconds: 0.5, axis: 0 }, { seconds: 0.35, axis: 1 }, { seconds: 0.9, axis: 0 }],
+  // Let go for a moment and hold again: the run timer restarts, so the body slows to a walk, then runs again.
+  'walk-run-walk-run': [{ seconds: 1.4, axis: 1 }, { seconds: 0.05, axis: 0 }, { seconds: 1.0, axis: 1 }, { seconds: 0.9, axis: 0 }],
+  'idle-run-idle': [{ seconds: 0.4, axis: 0 }, { seconds: 1.4, axis: 1 }, { seconds: 1.1, axis: 0 }],
+  'idle-jump-land': [{ seconds: 0.4, axis: 0 }, { seconds: 1.5, axis: 0, jump: true }],
+  'run-jump-land-run': [{ seconds: 1.0, axis: 1 }, { seconds: 1.4, axis: 1, jump: true }],
+};
+
+const STEP = 1 / 120;
+const out: Record<string, unknown> = {};
+for (const [name, phases] of Object.entries(SCRIPTS)) {
+  const body = { x: 0, y: 0, vx: 0, vy: 0, grounded: true };
+  const motion = movement(), air = jumpState(0), animation = new LocomotionAnimation(clips, () => 0.5);
+  const frames: { t: number; x: number; y: number; board: string; frame: string; pose: MotionPose }[] = [];
+  let t = 0;
+  for (const phase of phases) {
+    if (phase.jump) { body.vy = -JUMP_SPEED; body.grounded = false; air.active = true; air.origin = body.y; }
+    for (let n = 0; n < Math.round(phase.seconds / STEP); n++) {
+      const wasGrounded = body.grounded;
+      move(motion, phase.axis, STEP);
+      body.vx = motion.vx;
+      body.x += body.vx * STEP;
+      if (!body.grounded) {
+        body.vy += GRAVITY * STEP; body.y += body.vy * STEP;
+        if (body.y >= 0) { body.y = 0; body.vy = 0; body.grounded = true; }
+      }
+      landing(body, air, wasGrounded, STEP, times);
+      // player.ts's choice of pose, on flat ground with no ladder.
+      const desired: MotionPose = air.landing > 0 ? air.hard ? 'hard-landing' : 'land'
+        : !body.grounded ? body.vy < 0 ? 'jump' : 'fall'
+        : Math.abs(body.vx) > (WALK_SPEED + RUN_SPEED) / 2 ? 'run' : Math.abs(body.vx) > 5 ? 'walk' : 'idle';
+      const pose = animation.update(desired, STEP, Math.abs(body.vx), { vy: body.vy, launch: JUMP_SPEED });
+      frames.push({ t: +t.toFixed(4), x: +body.x.toFixed(2), y: +body.y.toFixed(2), ...pose, pose: desired });
+      t += STEP;
+    }
+  }
+  out[name] = frames;
+}
+process.stdout.write(JSON.stringify(out));
diff --git a/game/verification/transitions/walk-run-walk-run.gif b/game/verification/transitions/walk-run-walk-run.gif
new file mode 100644
index 0000000..c2c296d
Binary files /dev/null and b/game/verification/transitions/walk-run-walk-run.gif differ
diff --git a/scripts/test_transition_gifs.py b/scripts/test_transition_gifs.py
new file mode 100644
index 0000000..a3b7576
--- /dev/null
+++ b/scripts/test_transition_gifs.py
@@ -0,0 +1,24 @@
+"""Offline checks for transition_gifs.py: the 30 fps sampling of the 120 Hz trace, and where a frame is drawn."""
+import unittest
+
+import transition_gifs as tg
+
+
+class TransitionGifTests(unittest.TestCase):
+    def test_samples_every_fourth_step(self):
+        frames = [{"t": n / 120} for n in range(12)]
+        self.assertEqual([f["t"] for f in tg.samples(frames)], [0, 4 / 120, 8 / 120])
+
+    def test_place_puts_the_pivot_on_the_body(self):
+        # A 40x100 frame pivoted at its bottom centre, the body 10 px right of the camera and on the ground.
+        x, y = tg.place(110, 0, 100, (40, 100), (0.5, 1))
+        self.assertEqual((x + 20, y + 100), (tg.SIZE[0] // 2 + 10, tg.GROUND))
+
+    def test_place_lifts_a_body_in_the_air(self):
+        _, ground = tg.place(0, 0, 0, (40, 100), (0.5, 1))
+        _, air = tg.place(0, -30, 0, (40, 100), (0.5, 1))
+        self.assertEqual(ground - air, 30)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/scripts/transition_gifs.py b/scripts/transition_gifs.py
new file mode 100644
index 0000000..995b4c9
--- /dev/null
+++ b/scripts/transition_gifs.py
@@ -0,0 +1,103 @@
+"""The hero's locomotion transitions as GIFs (#156 "Smooth transitions"), from the game's own code.
+
+    python scripts/transition_gifs.py                 # every transition -> game/verification/transitions/<name>.gif
+    python scripts/transition_gifs.py idle-walk-idle  # one
+
+game/verification/transitions/trace.ts runs movement.ts, jump.ts and animation.ts as player.ts wires them (flat
+ground, 120 Hz) and prints which frame shows where; this draws it at 30 fps, 2x, with the camera on the hero and
+ground ticks every foot that move with the world – a foot that slides against the ticks is a foot that slides
+in the game. Each GIF frame is labelled with the clip frame and the pose the body asked for.
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import subprocess
+import sys
+from pathlib import Path
+
+from PIL import Image, ImageDraw
+
+ROOT = Path(__file__).resolve().parents[1]
+SPRITES = ROOT / "game" / "public" / "assets" / "sprites"
+TRACE = ROOT / "game" / "verification" / "transitions" / "trace.ts"
+OUT = TRACE.parent
+FOOT = 13  # px per foot at stage scale (docs/04)
+STEP_HZ, GIF_FPS, ZOOM = 120, 30, 2
+SIZE, GROUND = (300, 250), 230  # stage px; the ground line's y (room above for the 96 px jump)
+PAPER, INK, TICK = (236, 230, 216), (60, 52, 46), (150, 140, 128)
+
+
+def trace() -> dict[str, list[dict]]:
+    """Run trace.ts with node (type transforms on: animation.ts has parameter properties)."""
+    out = subprocess.run(["node", "--experimental-transform-types", "--no-warnings", str(TRACE)],
+                         capture_output=True, check=True, cwd=ROOT)
+    return json.loads(out.stdout.decode("utf-8"))
+
+
+def samples(frames: list[dict], step_hz: int = STEP_HZ, fps: int = GIF_FPS) -> list[dict]:
+    """Every step_hz/fps-th traced step: what a 30 fps capture of the 120 Hz game would show."""
+    every = max(1, round(step_hz / fps))
+    return frames[::every]
+
+
+def place(x: float, y: float, cam: float, size: tuple[int, int], pivot: tuple[float, float]) -> tuple[int, int]:
+    """Top-left of a frame whose pivot sits at body (x, y): x relative to the camera's centre, y up from the ground."""
+    w, h = size
+    return round(SIZE[0] / 2 + (x - cam) - pivot[0] * w), round(GROUND + y - pivot[1] * h)
+
+
+class Atlases:
+    def __init__(self) -> None:
+        self.cache: dict[str, tuple[Image.Image, dict]] = {}
+
+    def frame(self, board: str, name: str) -> tuple[Image.Image, tuple[float, float]]:
+        if board not in self.cache:
+            data = json.loads((SPRITES / f"{board}.json").read_text(encoding="utf-8"))
+            self.cache[board] = (Image.open(SPRITES / f"{board}.png").convert("RGBA"), data["frames"])
+        sheet, frames = self.cache[board]
+        if name not in frames:
+            sys.exit(f"{board} has no frame {name}")
+        r, pivot = frames[name]["frame"], frames[name].get("pivot", {"x": 0.5, "y": 1})
+        return sheet.crop((r["x"], r["y"], r["x"] + r["w"], r["y"] + r["h"])), (pivot["x"], pivot["y"])
+
+
+def draw(name: str, frames: list[dict], atlases: Atlases) -> Path:
+    pictures = []
+    for f in samples(frames):
+        cam = f["x"]
+        picture = Image.new("RGBA", SIZE, PAPER + (255,))
+        pen = ImageDraw.Draw(picture)
+        pen.line([(0, GROUND), (SIZE[0], GROUND)], fill=INK)
+        first = int((cam - SIZE[0] / 2) // FOOT) * FOOT
+        for wx in range(first, int(cam + SIZE[0] / 2) + FOOT, FOOT):
+            sx = round(SIZE[0] / 2 + wx - cam)
+            pen.line([(sx, GROUND + 1), (sx, GROUND + (6 if wx % (FOOT * 5) == 0 else 3))], fill=TICK)
+        sprite, pivot = atlases.frame(f["board"], f["frame"])
+        picture.alpha_composite(sprite, place(f["x"], f["y"], cam, sprite.size, pivot))
+        pen.text((4, 3), f"{f['frame']}", fill=INK)
+        pen.text((4, 14), f"pose {f['pose']}  t {f['t']:.2f}s", fill=TICK)
+        pictures.append(picture.convert("RGB").resize((SIZE[0] * ZOOM, SIZE[1] * ZOOM), Image.NEAREST))
+    # One palette for the whole GIF (the hero's colours plus paper and ink), so frames don't flicker or bloat.
+    palette = pictures[len(pictures) // 2].quantize(colors=96, method=Image.Quantize.MEDIANCUT)
+    frames_p = [picture.quantize(palette=palette, dither=Image.Dither.NONE) for picture in pictures]
+    path = OUT / f"{name}.gif"
+    frames_p[0].save(path, save_all=True, append_images=frames_p[1:], duration=round(1000 / GIF_FPS), loop=0,
+                     optimize=True)
+    return path
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument("names", nargs="*", help="transitions to draw (default: all of trace.ts)")
+    args = parser.parse_args()
+    traces, atlases = trace(), Atlases()
+    for name in args.names or traces:
+        if name not in traces:
+            sys.exit(f"trace.ts has no transition {name}: {', '.join(traces)}")
+        path = draw(name, traces[name], atlases)
+        print(f"{path.relative_to(ROOT).as_posix()}: {len(samples(traces[name]))} frames")
+
+
+if __name__ == "__main__":
+    main()