Domain: Healthcare — Nutrition & Dietetics
Target concept: Yeast Fermentation Balloons: Lactose Solution versus Lactose Plus Lactase Solution

Video generation prompt: Two transparent bottles containing lactose and yeast are placed side by side, each covered with an identical balloon; liquid lactase is added only to the right bottle, and the process is recorded without interference.

Evaluation guide:
(i) Target concept: Enzymatic substrate specificity enabling fermentable sugar release for microbial CO₂ production.
Minimum mechanism: Lactase must be present and active; yeast must be viable and capable of fermenting monosaccharides (but not lactose); lactose solution must be non-fermentable without hydrolysis; CO₂ production must be visually trapped by balloon inflation.
(ii)Storyline: [Frame 0–2] Two sealed bottles with identical flat balloons in static side-by-side view; [Frame 3–4] Hand enters frame from bottom, holds lactase dropper above right bottle mouth; [Frame 5] Lactase liquid contacts right bottle solution (visible meniscus disturbance); [Frame 6–10] Right balloon progressively expands upward/outward; left balloon remains unchanged in shape, position, and tautness; entire scene maintains fixed camera perspective, consistent lighting, and no occlusion violations.

Manual:
Experimental Procedure
1. Place two identical transparent bottles side-by-side on a flat surface.
2. Fill both bottles with equal volumes of lactose solution and active yeast suspension.
3. Stretch identical uninflated balloons over the mouths of both bottles, sealing tightly.
4. Add liquid lactase only to the right bottle (no addition to left).
5. Record continuously for 10 seconds with fixed frontal viewpoint.
Observation of Experimental Phenomena
The balloon on the right bottle inflates visibly (expands upward and outward), while the balloon on the left bottle remains flat and relaxed—no inflation observed within 10 seconds.
Summary of Experimental Principles
Lactase hydrolyzes lactose into glucose and galactose, which yeast metabolizes via fermentation, producing CO₂ gas. Without lactase, lactose remains unfermentable by most yeast strains; thus, no CO₂ is generated in the left bottle.

Prompt Grounding rubric:
level_1: Fewer than two bottles appear, or one or both bottles lack a balloon stretched over the mouth, or the lactase-adding action never happens on screen, or the two bottles are never shown together in one shot, or neither bottle contains any visible liquid.
level_2: Two bottles with balloons appear, but at least one required setup element is wrong: one bottle is opaque or a different container type, one balloon is missing or clearly deflated/torn from the start, the lactase drops are added to both bottles or to neither, or the two bottles are arranged one behind the other rather than beside each other.
level_3: Two transparent bottles sit side by side, each sealed with an intact balloon over its mouth, both bottles contain a cloudy liquid consistent with a lactose-and-yeast suspension, and a hand adds liquid lactase from a dropper into the right bottle only, with no lactase reaching the left bottle.
level_4: Everything required for a 3-score is present, and in addition: the camera keeps a fixed left/right framing so which bottle is 'right' never changes or mirrors, the lactase is added in a single clear pour/drop action (not sprayed, poured as powder, or otherwise ambiguous), and both balloons stay securely attached to their bottle necks for the whole video.
level_5: Everything required for a 4-score is present, and in addition: the hand adding lactase never touches or disturbs the left bottle at the same time, neither bottle carries any text label, sticker, or color cue that would reveal which one is which beyond their left/right position, and the camera holds one continuous, unobstructed view of both bottles and balloons for the entire recording.

Scientific and Causal Correctness rubric:
level_1: Neither balloon inflates at all, or both balloons inflate by a similar amount, or the left balloon inflates while the right stays flat, or the liquid in either bottle shows no sign of yeast activity (no cloudiness or suspended particles) from the very start.
level_2: The right balloon begins to inflate while the left stays flat, but the inflation starts before the lactase drop ever reaches the right bottle's liquid, or the left bottle's liquid also shows visible bubbling or foaming despite receiving no lactase.
level_3: The right balloon visibly expands and gains tautness only after the lactase drop reaches the right bottle, while the left balloon stays flat and unchanged for the whole video, with no deflation or reversal of the right balloon once it starts inflating.
level_4: Everything required for a 3-score holds, and in addition: the right balloon's inflation grows steadily larger over time rather than pausing, shrinking, or fluttering, and the left balloon shows no size change whatsoever, not even a slight lift or wobble.
level_5: Everything required for a 4-score holds, and in addition: the right balloon expands symmetrically upward and outward from the bottle mouth rather than bulging to one side, the balloon-to-bottle seal shows no gap or wrinkle suggesting a gas leak, and the left balloon remains flush against the bottle rim in its original flat shape through the final frame.

Spatiotemporal Consistency rubric:
level_1: A bottle or balloon jumps to a new position or vanishes from the frame between shots, the lactase liquid appears already inside the right bottle with no visible drop or pour, the right balloon snaps from fully flat to fully inflated within a single frame, or the lighting abruptly shifts (e.g., a flash or sudden darkening) with no visible cause.
level_2: The dropper's lactase stream is missing its motion (liquid appears mid-air with no trajectory from dropper to bottle mouth), the camera angle or zoom changes noticeably partway through, or the bottle outlines visibly warp or bend across frames.
level_3: Both bottles stay in the same side-by-side spot for the entire video, the lactase drop travels with continuous, visible motion from the dropper into the right bottle's mouth, and neither bottle nor balloon changes shape abruptly outside of the right balloon's gradual inflation.
level_4: Everything required for a 3-score holds, and in addition: the frame-to-frame motion is smooth with no repeated or skipped frames, the balloon material and the liquid's surface keep a consistent look across frames (no flickering transparency or sudden sheen changes), and background elements behind the bottles do not slide independently of the bottles themselves.
level_5: Everything required for a 4-score holds, and in addition: the lactase droplet's path curves naturally rather than moving in a rigid straight line, the right balloon's size increases at a steady, gradual pace rather than jumping between sizes, and the hand that adds the lactase never reappears in front of or behind the bottles in a way that breaks the established depth order.