Domain: Healthcare — Human Physiology
Target concept: The effect of cold stimulation on vasoconstriction

Video generation prompt: A hand is immersed in cold water, while the other hand remains at room temperature. Keep both hands clearly and continuously visible before immersion, during the brief cold stimulus, and after removal. Use simple steps and clear hand movements.

Evaluation guide:
(i) Target concept: Reversible, localized, stimulus-dependent vasoconstrictive pallor in human skin.
Minimum mechanism: Intact autonomic innervation to cutaneous vasculature; functional thermoreceptors; intact microcirculation; no underlying peripheral vascular disease or pigmentary abnormality.
(ii)Storyline: Phase 1 (Baseline): Both hands stationary, side-by-side, identically lit, showing normal skin tone. Phase 2 (Stimulus Onset): Left hand moves into cold water container; within same continuous motion sequence, pallor emerges on immersed hand surface while right hand remains unchanged. Phase 3 (Stimulus Offset): Left hand exits water; pallor begins resolving progressively during after-removal rest. Perspective constraint: Fixed frontal, eye-level camera; no zoom, pan, or rotation; hands and container fully in frame at all times; lighting stable and diffuse.

Manual:
Experimental Procedure
1. Place two bare human hands side-by-side in frame, palms facing up, resting on neutral surface.
2. Bring a transparent container filled with cold water into view; immerse left hand fully into water while right hand remains stationary and dry.
3. Hold immersion for brief duration, then remove left hand and return both hands to original side-by-side rest position.
Observation of Experimental Phenomena
- During immersion: left hand skin appears paler (less ruddy, more desaturated) than right hand.
- Before and after immersion: both hands display comparable baseline skin tone.
- Side-by-side visibility confirms contrast is due to stimulus, not lighting or angle.
Summary of Experimental Principles
Cold stimulation triggers sympathetic-mediated vasoconstriction in cutaneous arterioles, reducing blood flow and surface perfusion — clinically observed as pallor. This is reversible upon rewarming.

Prompt Grounding rubric:
level_1: No hands are visible at all, or only one hand appears in frame; no water container is present; there is no moment where a hand goes into the water; the two hands are never shown together for comparison; or the clip skips straight past one of the three phases (before/during/after).
level_2: Only one hand shows up during any given phase; the two hands are never both in frame at the same time for comparison; a water container appears but no hand is ever shown touching the water; only two of the three phases (before, during, after) are shown, with one missing entirely; a hand is cropped out of frame or otherwise not clearly identifiable as a hand.
level_3: Both hands appear together in at least one frame; a container holding visible liquid is present; at least one hand touches the water in at least one frame; all three phases (before immersion, during immersion, after removal) appear in that order; both hands are clearly identifiable and positioned so they can be compared side by side.
level_4: Everything in the 3-point description holds, and in addition: both hands stay fully within the camera frame, not cut off at the edge, across all three phases; the water container is clearly a distinct object (e.g., see-through or otherwise identifiable), not blended into the background; the moment of the hand entering or sitting in the water is unambiguous; nothing else in the shot draws attention away from the hands or container.
level_5: Everything in the 4-point description holds, and in addition: the left hand and the right hand are set up side-by-side, each on its own side of the frame, with the cold-water container placed so both hands remain clearly comparable to it; the container is unobstructed and clearly visible whenever it is in shot; neither hand nor the container is spliced into or edited out of the shot partway through the clip.

Scientific and Causal Correctness rubric:
level_1: Neither hand shows any skin-tone change throughout the clip; or both hands look the same in every phase; or the pattern runs backward: the immersed hand looks redder or more flushed while the dry hand goes pale; or the dry hand pales more than the immersed one.
level_2: Only one hand ever shows a skin-tone change, with no clear comparison shown for the other; or pallor only shows up after the hand is already removed rather than during immersion; or the immersed hand darkens or discolors in a way that does not read as simple pallor (e.g., uneven blotchy or bruise-like darkening); or both hands are visible together but never show a visible tonal difference.
level_3: The immersed hand turns visibly paler (lighter and less ruddy) during the cold-water phase; the dry hand keeps its normal warm skin tone at the same time; both hands being shown together makes the tonal difference clear; the immersed hand's color moves at least partway back toward its baseline once removed from the water.
level_4: Everything in the 3-point description holds, and in addition: the paleness affects the skin evenly rather than concentrating oddly at the nails or knuckles; there is no unnatural tint such as a bluish or yellowish cast, or blotchy patches; the dry hand shows no paling at all, at any point; the immersed hand's color is visibly less pale by partway through the after-removal phase than it was during immersion.
level_5: Everything in the 4-point description holds, and in addition: the paling begins right as the hand goes under the water, not noticeably before or after; once removed, the color keeps recovering steadily through the after-removal phase without dipping back toward pale again; the tonal gap between the two hands is largest during immersion and steadily shrinks afterward; nothing else on screen (a lighting change, a shadow, a reflection) could be mistaken for the pallor itself.

Spatiotemporal Consistency rubric:
level_1: A hand or the water container jumps to a different spot or vanishes and reappears with no visible movement leading there; a hand splits, merges, or bends in an anatomically impossible way; the lighting swings from fully lit to near-total shadow within a single frame.
level_2: A hand visibly drifts or trembles more than normal handheld unsteadiness would explain; either hand is hidden from view for more than two frames in a row with nothing shown blocking it; the water container shifts position with no hand or other support moving it; the clip stutters or freezes for a beat with no clear cause.
level_3: Neither hand nor the container disappears, splits, or bends unnaturally; each hand keeps roughly the same orientation and position relative to the frame except for the deliberate immersion/removal motion; the main light source stays in the same direction throughout; shadows stay attached to the hands and container in a plausible way; the immersed hand moves downward into the water rather than sliding in sideways.
level_4: Everything in the 3-point description holds, and in addition: neither hand is hidden from view for more than a single frame at a time; no lighting change alters how pale or flushed the skin looks apart from the physiological response itself; the relative size and depth of the two hands and the container stay believable frame to frame; the immersion and removal motions play out smoothly, without stutters or sudden jumps in speed.
level_5: Everything in the 4-point description holds, and in addition: the position and framing of both hands and the container stay visually steady across every cut or transition, with no drift or rescaling; ambient lighting and color stay constant except where a hand's own motion naturally casts a new shadow; every hand and arm movement follows a natural, gradually accelerating and decelerating motion; hands and the container never appear to pass through one another.