Domain: Healthcare — Skin Physiology
Target concept: Skin pH Measurement

Video generation prompt: An adult male placed his left forearm on a table and gently touched the skin with a pH indicator paper, maintaining contact between the paper and the skin for several seconds. Subsequently, the color of the pH paper was compared with a color chart to determine the pH value.

Evaluation guide:
(i) Target concept: Non-invasive, visual determination of skin surface acidity via reversible acid-base indicator chemistry.
Minimum mechanism: pH indicator dye must be immobilized on porous paper substrate; skin surface must provide sufficient moisture and H+ ions to induce protonation/deprotonation; ambient lighting must enable color discrimination; chart must encode empirically validated pH-color mapping.
(ii)Storyline: Frame 1–3: Forearm settles onto table (stable base established). Frame 4–6: Paper approaches and makes full, flush contact with skin (no air gaps). Frame 7–9: Paper remains motionless in contact (color development phase). Frame 10–12: Paper lifts cleanly and rotates/translates to align beside chart (no occlusion). Frame 13–15: Paper and chart held static, side-by-side, under consistent lighting (comparison phase). All phases observed from fixed frontal-midrange viewpoint capturing forearm, paper, and chart in full frame without cutaways or perspective shifts.

Manual:
Experimental Procedure
1. Adult male places left forearm flat on table surface.
2. He gently presses pH indicator paper against forearm skin and holds contact steadily.
3. After several seconds, he lifts paper and holds it beside a standardized pH color chart for direct visual comparison.
Observation of Experimental Phenomena
pH indicator paper changes from beige to stable amber/orange color upon skin contact; this color matches a labeled swatch (e.g., pH 5.5) on the chart.
Summary of Experimental Principles
Healthy human skin surface has weakly acidic pH (4.5–6.0); pH indicator paper contains dyes that reversibly change hue in response to H+ ion concentration; color comparison to calibrated chart yields semi-quantitative pH value.

Prompt Grounding rubric:
level_1: No adult male present; no left forearm visible; no table surface; no pH indicator paper; no color chart; none of the required objects appear.
level_2: At least one of the following appears: adult male, left forearm, table, pH indicator paper, or color chart; but fewer than three core objects are present, and zero correct sequential actions (e.g., paper not touching skin, no comparison gesture).
level_3: All five core objects are present: adult male, left forearm, table, pH indicator paper, and color chart. The forearm is placed on the table, and the paper contacts the forearm skin, but no visible comparison between paper and chart occurs.
level_4: All five core objects present and correctly positioned: left forearm rests on table; pH indicator paper is in direct contact with forearm skin; paper is then visibly held adjacent to color chart for side-by-side visual comparison, but either the paper-skin contact duration is not sustained (paper lifts before stable color appearance), or the chart is partially occluded or misoriented (not facing camera clearly).
level_5: All five core objects present and fully compliant: adult male’s left forearm fully rests on table surface; pH indicator paper is flat and fully contacting forearm skin for a continuous, unbroken duration; immediately after contact, the same paper is held stably and fully visible beside an intact, upright, legible color chart with both paper and chart simultaneously in clear view and aligned for direct side-by-side color comparison.

Scientific and Causal Correctness rubric:
level_1: pH paper shows no color change upon skin contact; or paper displays a color inconsistent with human skin pH range (e.g., bright blue, deep red, purple); or chart displays no color gradients or uses non-standard hues (e.g., grayscale, rainbow without pH scale labels).
level_2: pH paper changes color upon contact, but the resulting color does not match any hue on the visible chart; or chart is present but lacks discernible pH-numbered color swatches; or paper color remains unchanged while chart is shown.
level_3: pH paper changes to a color within typical skin pH range (yellow-to-amber-to-light brown); chart displays standard pH color progression (e.g., yellow = pH 4.0–5.0, orange = 5.0–5.5, light brown = 5.5–6.0); paper and chart are both visible, but no causal link is visually verifiable (e.g., paper lifted before color stabilizes, or chart viewed without paper beside it).
level_4: pH paper changes to a stable, uniform color consistent with healthy skin pH (i.e., amber/orange/buff tone); chart displays correctly ordered, labeled pH swatches; paper is held adjacent to chart with matching hue region clearly aligned, but either the paper color is uneven (patchy, streaked), or one swatch on chart is illegible due to blur/occlusion.
level_5: pH paper exhibits a uniform, solid, stable color post-contact (no fading, bleeding, or gradient); that color exactly matches one labeled swatch on the chart (e.g., amber paper aligns with “pH 5.5” swatch); both paper and matched swatch are fully in focus, fully visible, and identically lit; no discoloration, smudging, or mismatched saturation between paper and swatch.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal violations: forearm teleports from air to table; paper appears/disappears mid-air; chart rotates >90° without motion continuity; lighting flickers or shifts abruptly between frames; table surface warps or fractures.
level_2: Moderate violations: forearm placement and paper contact occur in separate shots with mismatched lighting/shadow direction; paper moves discontinuously (jumps, skips, or freezes >3 frames); chart enters frame from off-screen with no establishing motion; skin surface distorts during contact (e.g., unnatural stretching or pixelation).
level_3: Minor but detectable violations: paper briefly loses full contact (edge lifts) during hold phase; chart shifts slightly (<10% frame width) between paper-contact and comparison phases; shadow under forearm changes intensity without lighting source movement; all objects remain in fixed relative positions but lack smooth transition between contact and comparison.
level_4: All objects maintain consistent spatial relationships throughout: forearm remains stationary on table; paper maintains full, flat contact without lifting or sliding; chart remains fixed in position and orientation; lighting and shadows remain stable; only natural micro-movements (e.g., slight hand tremor) occur: no structural breaks or temporal jumps.
level_5: Zero spatiotemporal flaws: forearm position, paper placement, chart location, lighting geometry, and shadow alignment remain absolutely invariant across all frames; paper contact is initiated and maintained with continuous, fluid motion; transition from contact to comparison occurs in a single unbroken shot with no cut, zoom, or reframe; all object edges remain crisp and geometrically stable.