Domain: Natural Science — Atmospheric Science
Target concept: Carbon dioxide from exhaled air dissolves in the indicator solution, causing a color change (carbonation).

Video generation prompt: Two transparent cups containing blue bromothymol blue solution are placed on the experimental table; a person blows into the cup on the left through a straw, while the cup on the right remains untouched.

Evaluation guide:
(i) Target concept: Acidification-driven pH indicator color transition induced by CO₂ dissolution.
Minimum mechanism: Exhaled air must contain sufficient CO₂; solution must be aqueous bromothymol blue at appropriate concentration and initial pH (~7.6) to be blue; dissolution must occur in left cup only; no contamination or alternative acid source.
(ii)Storyline: Frame 0–1: Static shot showing two identical blue-filled cups side-by-side, straw resting in left cup, person poised. Frame 2–3: Person initiates blowing: visible jaw/cheek motion, straw aligned, left cup liquid surface begins subtle ripple. Frame 4–7: Left cup color progressively shifts from blue → green → yellow-green; right cup remains uniformly blue; no contact with right cup; no spillage. Frame 8–9: Blowing ceases; left cup holds new color; right cup unchanged; final frame confirms side-by-side contrast. Perspective: Fixed frontal medium shot, full cups in frame, no cutaways or zooms.

Manual:
Experimental Procedure
1. Place two transparent cups side-by-side on a table.
2. Fill both cups with blue bromothymol blue solution.
3. Insert a straw into the left cup.
4. Blow steadily into the straw for ~3 seconds.
5. Observe both cups simultaneously.
Observation of Experimental Phenomena
The left cup changes from blue to green or yellow-green; the right cup remains unchanged and stays blue.
Summary of Experimental Principles
Carbon dioxide from exhaled air dissolves in the indicator solution, forming carbonic acid, lowering pH and causing bromothymol blue to shift from blue (basic) to green/yellow-green (acidic).

Prompt Grounding rubric:
level_1: No two cups of blue liquid are shown; no straw or blowing action appears; no person is present; the two cups are not shown positioned next to each other on the table.
level_2: Two containers appear, but not matching the setup: only one holds liquid, or the liquid isn't blue; a straw appears but doesn't reach into the left cup; a person is shown but isn't blowing; or the cups are stacked, far apart, or otherwise not placed side by side.
level_3: Two transparent cups sit side by side on a flat surface, each filled with visibly blue liquid; a straw sits in the left cup; a person's mouth is positioned near the straw; the right cup has nothing touching it; no other prop (labels, gloves, unrelated tools) dominates the shot.
level_4: Everything in score 3 holds, and: the person is shown actively blowing, cheeks compressed, posture indicating a steady exhale (visible breath fog is not required); the straw stays seated in the left cup the whole time; the right cup receives no hand, tool, or contact of any kind.
level_5: Everything in score 4 holds, and: the blowing clearly starts before any color change appears in either cup; only the left cup ever receives air through the straw: no second straw, no accidental contact with the right cup, and neither cup nor the straw is repositioned mid-action; the camera keeps both cups fully in view at once, with nothing cropped or blocked throughout.

Scientific and Causal Correctness rubric:
level_1: Neither cup ever changes color; or the left cup's blue shifts to a hue bromothymol blue cannot show under acidification (e.g., blue to red or blue to purple); or it is the right, untouched cup that changes instead of the left.
level_2: A color change happens but breaks the mechanism: only the right cup changes; the left cup changes with no blowing action shown; the left cup jumps straight from blue to yellow without ever passing through green; both cups change identically at the same time; or the color reads as opaque white or black rather than a genuine blue-green-yellow shift.
level_3: The left cup visibly changes from blue toward green or yellow-green; the right cup stays a stable blue throughout; the left cup's change starts only after blowing begins and moves gradually rather than jumping instantly; neither cup's color flickers or reverses partway through.
level_4: Everything in score 3 holds, and: the left cup's color change stays confined to that cup, with no splashing or spreading of altered liquid into the right cup; the table, background, or reflections show no matching color shift; the right cup's blue stays even in hue and saturation throughout.
level_5: Everything in score 4 holds, and: the left cup's blue passes visibly through green before reaching yellow-green, without ever skipping straight to yellow; the color shows no graying-out or bleached look; the right cup's blue matches the left cup's original blue in hue and intensity; the color change is never shown starting before the first frame depicting the person blowing.

Spatiotemporal Consistency rubric:
level_1: A cup vanishes in one frame and reappears in another; the straw or the person appears or disappears with no matching action; the lighting swings sharply between frames (a sudden switch from lit to dark); a cup's shape warps or breaks apart; or the liquid's surface jumps to a new state or freezes mid-splash with no continuous motion leading there.
level_2: A straw's tip vanishes for a couple of frames then comes back; one cup gets briefly hidden by the hand or body and doesn't reappear cleanly; a cup's transparency flickers on and off momentarily; or the liquid's meniscus shape changes abruptly between frames (convex, then flat, then concave) with no visible cause.
level_3: Both cups stay fully visible and intact throughout; the straw stays seated in the left cup at a consistent depth and angle; the person's head and upper body hold a coherent position; the liquid surfaces show only gentle, low-amplitude ripple during blowing with no structural break; any shift in lighting or shadow tracks the visible motion in the scene rather than appearing arbitrary.
level_4: Everything in score 3 holds, and: each cup's rim stays a consistent round shape rather than flexing into an ellipse or wobbling; background elements shift consistently with any camera movement; the liquid never behaves implausibly (no floating above the cup, no shearing flow, no ripple that persists on its own after the blowing stops).
level_5: Everything in score 4 holds, and: the person's blowing motion reads as one continuous action: a slight jaw drop, then cheek compression with steady straw contact, then release; the left cup's liquid responds with a ripple that grows and settles in proportion to the blowing; there's no frame duplication, stutter, or interpolation glitch; the cups, straw, and person keep consistent spatial relationships to one another across the whole sequence.