Domain: Healthcare — Skin Physiology
Target concept: Blood Flow Regulation

Video generation prompt: A subject with fair skin clenched their fist for 3 seconds and then released it, while the camera was focused on the subject's hand to observe changes in finger color.

Evaluation guide:
(i) Target concept: Capillary refill in the fingertips as a visible indicator of normal digital blood flow, following brief mechanical compression of the digital vessels during a fist clench.
Minimum mechanism: Intact digital artery inflow, a compressible capillary bed in the finger pulp, and normal vasomotor tone sufficient for prompt capillary refill once the compressing grip is released; a brief (few-second) clench is expected to produce simple mechanical blanching followed by ordinary capillary refill back toward baseline color, not a sustained ischemia-driven hyperemic overshoot beyond baseline.
(ii)Storyline: [Phase 1: Baseline] Fair-skinned hand rests motionless, fingers extended, pulp/tips showing natural rosy-pink hue. [Phase 2: Clench] Fingers flex fully into fist; knuckles rise, palmar surface compresses; pulp/tips lose saturation and become uniformly pale/ashen; no discoloration elsewhere. [Phase 3: Release] Fingers extend synchronously and fully; pulp/tips rapidly regain rosy-pink hue with identical spatial distribution as baseline; no delayed or patchy reperfusion. Perspective: Fixed frontal view centered on hand; full finger pulp/tips must remain unobstructed and in-focus throughout all phases.

Manual:
Experimental Procedure
1. Subject with fair skin places hand flat on neutral background, palm down.
2. Subject tightly clenches fist for duration sufficient to induce capillary compression (visually sustained grip).
3. Subject fully releases fist and holds hand still.
Observation of Experimental Phenomena
During clenching: finger pulp and tips visibly pallor (lighten to pale/ashen tone).
After release: finger pulp and tips visibly redden (return to rosy-pink tone) within same regions.
Summary of Experimental Principles
Clenching compresses digital arteries and capillaries → brief local ischemia → visible pallor in the finger pulp. Releasing the grip immediately restores blood flow, and capillary refill brings the pulp back to its normal rosy-pink baseline color. This demonstrates simple mechanical blood displacement and capillary refill in skin microcirculation; a brief clench of only a few seconds is not expected to trigger a sustained ischemia-driven reactive-hyperemia overshoot beyond baseline coloration.

Prompt Grounding rubric:
level_1: No hand is visible at any point, or the visible hand never actually clenches into a fist and never releases, or the camera is not looking at a hand (e.g., wrong body part in frame or hand off-screen for most of the clip), or the hand clearly does not belong to a fair-skinned person (e.g., visibly medium or dark-brown skin tone).
level_2: A hand is in frame, but its skin tone is not clearly fair (e.g., medium-brown, tan, or otherwise not light-toned), or the fist-clench action is missing or replaced by an unrelated gesture (waving, tapping, pointing), or there is no distinct release following the clench, or the camera view swings away from the hand or loses focus on it for a noticeable stretch.
level_3: A fair-skinned hand stays in frame for the whole clip; the fingers fully curl into a closed fist at some point and later fully open again (release); the camera keeps the hand in steady focus throughout; the finger pulp and tips stay visible and unobstructed (not hidden behind the thumb, other fingers, or an object) so their color can be judged.
level_4: All conditions for score 3 are satisfied, and additionally: the hand stays clenched for a clearly longer stretch than the brief moment of releasing (the clench is held, the release is quick), and after releasing, the fingers settle into a fully relaxed open position without lingering partial curling.
level_5: All conditions for score 4 are satisfied, and additionally: all five fingers close into the fist together (none lags noticeably behind the others), and on release all five open and spread apart together (no single finger straightening late or staying curled); the hand stays in roughly the same spot on screen the whole time, without visibly drifting across the frame or rotating to a different angle.

Scientific and Causal Correctness rubric:
level_1: No visible color change occurs in the fingers at any point (the pulp and tips stay the same rosy-pink shade throughout clench and release), or the color change runs backward: the fingertips turn redder/darker while the fist is clenching and only turn paler/lighter after the hand releases.
level_2: A color change happens, but it does not track the compression/release cycle correctly: for example, the paling only begins after the hand has already released rather than during the clench itself, or the color change shows up on the back of the hand or under the fingernails rather than on the fleshy pulp/tips, or some fingers pale or redden while others show no change even though all fingers were clenched the same way.
level_3: While the fist is clenched, the finger pulp and tips visibly pale, lightening toward an ashen/whitish tone compared to baseline; within roughly a second or two after the hand opens, those same pulp/tip regions visibly redden back toward the original rosy-pink baseline color; the paling appears first at the pulp/tips rather than the palm or nails, and the reddening reappears in the same regions that paled.
level_4: All conditions for score 3 are satisfied, and additionally: the pale region stays confined to the pulp/tips and does not creep up past the last knuckle onto the palm; the reddening on release is likewise confined to those same pulp/tip areas and does not spread onto the palm or dorsal hand; the fingernails do not visibly change color during either phase.
level_5: All conditions for score 4 are satisfied, and additionally: the paling reads as an even, flat loss of color with no blotchy patches or bluish cast; the reddening on release reads as an even return to the original rosy-pink shade with no purple, yellow, or gray cast appearing along the way; the shift from pale to rosy-pink plays out as a smooth continuous change rather than jumping in one step; there is no obvious color fringe or halo along the finger edges during the transition.

Spatiotemporal Consistency rubric:
level_1: The hand vanishes from frame or is swapped for a visibly different hand between shots; the clip cuts abruptly mid-clench with a visible jump in the hand's position; fingers visibly melt, stretch, or fuse into each other; or the lighting on the hand changes abruptly (e.g., a sudden flash or the light source jumping to a different side) with no relation to the clench/release motion.
level_2: The hand stays on screen throughout, but shows a smaller structural break: the number of visible fingers changes at some point (e.g., only four are visible mid-clench, or a sixth digit briefly appears), the hand's apparent size suddenly jumps larger or smaller without the hand actually moving toward or away from the camera, or the hand's shadow on the background suddenly appears on the opposite side from where the light source is.
level_3: The hand keeps its five-fingered structure and normal proportions for the entire clip; there is no cut, freeze, or jump in the hand's position; the shadow the hand casts on the background stays on one consistent side and does not swap sides or disappear; no finger bends backward or at an anatomically impossible angle.
level_4: All conditions for score 3 are satisfied, and additionally: the knuckle contour at the base of the fingers changes smoothly as the fist closes and opens, without suddenly flattening or bulging unnaturally; the background behind the hand stays fixed and does not shift or warp as the hand moves; fingers do not visibly cross through each other or clip into the palm.
level_5: All conditions for score 4 are satisfied, and additionally: the fingers curl into the fist and unfurl again in a smooth, continuous motion rather than snapping shut or open in a single instantaneous jump; no blurring smears together which finger is which during the fastest part of the motion; the hand holds a steady position on screen throughout the clip, without visibly drifting or rotating.