Domain: Healthcare — Skin Physiology
Target concept: Arrector Pili Reflex (Cold)

Video generation prompt: Show a close-up view of a human forearm. A cold object — either a small metal item or an ice cube wrapped in cloth — is brought into brief contact with a small patch of forearm skin, held there briefly, and then lifted away. Focus only on the procedural steps of approach, contact, and removal, and on how the skin at that spot looks before, during, and after this contact.

Evaluation guide:
(i) Target concept: Cold-induced arrector pili reflex resulting in localized, transient piloerection on human forearm skin.
Minimum mechanism: Intact peripheral nerve signaling (A-delta and C fibers), functional sympathetic efferents, viable arrector pili smooth muscle, and normal pilosebaceous unit anatomy, sufficient to produce observable mechanical elevation of hairs upon thermal challenge.
(ii)Storyline: [Phase 1: Baseline] Static shot of relaxed forearm skin: smooth, flat, no texture elevation. [Phase 2: Stimulus Introduction] Cold object enters frame and makes physical contact with one small region of skin. [Phase 3: Response Onset] Within the same continuous visual segment, discrete bumps emerge *only* at contact site: no spread, no delay beyond contact initiation. [Phase 4: Stimulus Removal] Object lifts cleanly away from same site. [Phase 5: Response Persistence & Resolution] Piloerection remains visible briefly after removal, then gradually resolves; no new bumps appear elsewhere; no concurrent vasomotor or glandular activity. Perspective: Fixed frontal/slightly oblique view of forearm; full visibility of stimulated skin region throughout; no occlusion, no cuts, no viewpoint shifts.

Manual:
Experimental Procedure
1. Position human forearm in clear view, skin surface fully exposed.
2. Bring cold stimulus (metal object OR ice cube wrapped in thin cloth) into brief contact with a small area of forearm skin.
3. Maintain contact for a short duration, then fully remove stimulus.
Observation of Experimental Phenomena
- Before contact: smooth, flat skin texture with no visible hair elevation.
- During/after contact: localized piloerection — discrete, raised hair follicles forming visible bumps (gooseflesh) exclusively at the stimulated site.
Summary of Experimental Principles
- Cold stimulation activates cutaneous thermoreceptors at the contact site, triggering a localized sympathetic reflex confined to that skin segment rather than a whole-body hypothalamic thermoregulatory response; sympathetic nerve fibers cause arrector pili muscles in that same small region to contract, erecting the hair follicles there and producing piloerection restricted to the stimulated area.

Prompt Grounding rubric:
level_1: The video does not show a human forearm at all, or shows no cold-stimulus object (no metal implement, no cloth-wrapped ice cube), or never depicts the object touching the skin, or never depicts the object being lifted away; the basic setup of forearm plus cold object plus contact plus removal is missing entirely.
level_2: A forearm is shown, but the object used is not recognizable as a cold source (e.g., it is a warm object, a spray bottle, or a bare hand with no object at all); or the object touches the skin but is never withdrawn; or contact and removal are shown out of order (removal shown before any contact occurs).
level_3: A human forearm is clearly visible; a cold-stimulus object (a metal item or a cloth-wrapped ice cube) is shown; the object makes contact with a small patch of forearm skin; the object is then lifted away from the skin; these four elements (forearm, correct object, contact, removal) appear in this order.
level_4: All 3-point requirements are met, and in addition: the object's cold nature is visually indicated (e.g., a metallic sheen, or visible condensation/frost on the cloth wrapping the ice); contact is confined to a small patch of skin rather than the whole forearm or a non-skin surface such as a sleeve or fingernail; no unrelated object or hand gesture interrupts the forearm-object interaction.
level_5: All 4-point requirements are met, and in addition: the object keeps the same size, shape, and surface appearance from before contact through after contact (it does not morph into a different object); contact and removal both occur at the same patch of skin, not two different spots; the framing of the forearm stays fixed with no cuts or viewpoint changes across the approach-contact-removal sequence.

Scientific and Causal Correctness rubric:
level_1: No hair-bump texture (piloerection) appears anywhere on the forearm at any point; the skin looks the same before, during, and after the cold object touches it; or the skin instead shows an unrelated or opposite response such as sweating, reddening, or the hairs lying flatter than before.
level_2: Piloerection appears, but its timing does not match the stimulus: for example bumps appear before the object ever touches the skin, or appear and then stay unchanged regardless of removal; or the bumps spread across the whole forearm rather than staying only where the object touched; or bumps appear even though the object shown is not a cold one.
level_3: A patch of raised, bumpy skin (piloerection) appears only in the small area where the cold object made contact; the bumps are not visible before contact, become visible sometime between the start and end of contact, and are still visible for a brief period right after the object is removed.
level_4: All 3-point requirements are met, and in addition: the raised-bump patch has a clear edge and does not fade gradually into smooth skin further up the forearm; no unrelated skin change happens at the same time (no reddening, no sweat sheen, no flattened hair); the bump texture reads as fine, subtle forearm goosebumps rather than large or cartoonish spikes.
level_5: All 4-point requirements are met, and in addition: the bump patch becomes visible while the object is still touching the skin, without a noticeable delay after contact; the patch fades back to smooth skin sometime after the object is fully removed, with no bumps remaining by the end of the clip; the patch does not flicker on and off or partially appear/disappear between shots; the size, density, and location of the bumps match what a real cold touch would produce, confined to roughly the contact-sized patch, not the whole limb.

Spatiotemporal Consistency rubric:
level_1: The forearm or the cold object jumps to a different position or angle between shots with no motion connecting them; the forearm's shape breaks apart, warps, or part of it vanishes; the lighting on the skin suddenly flashes or shifts abruptly for no visible reason; the contact and the removal appear to happen in two different scenes or camera angles that don't match.
level_2: The forearm stays on screen but its shape stretches, squashes, or wobbles unnaturally; the cold object blinks in and out of view instead of moving continuously; the color or direction of the light on the skin changes suddenly partway through the clip for no visible reason; the object contacts the skin at one location (e.g., near the wrist) but is shown lifting away from a different location (e.g., near the elbow).
level_3: The forearm stays fully on screen and keeps a normal, intact shape throughout; the cold object moves smoothly toward the skin, pauses in contact, and smoothly lifts away; the lighting on the skin looks the same in color and brightness from the start of the clip to the end; the object touches and lifts away from the same patch of skin, with no jump, warp, or missing body part.
level_4: All 3-point requirements are met, and in addition: the object's path toward and away from the skin looks like a natural hand or arm movement rather than an impossible angle; the object does not shake or double-image as it moves; the forearm's skin surface keeps the same texture throughout without shimmering or breaking up; the framing does not zoom, pan, or rotate during the sequence.
level_5: All 4-point requirements are met, and in addition: the object's approach and withdrawal move at a steady, believable speed with no sudden jump in speed and no instant stop/start as if teleporting; where the object presses into the skin, the skin dents and springs back the way soft tissue would, rather than staying perfectly rigid or distorting oddly; the whole motion looks smooth and continuous from first approach to final withdrawal, without any visible freezing or stutter.