Domain: Healthcare — Nutrition & Dietetics
Target concept: Effect of Fermentation on Food Acidity (Yogurt Fermentation)

Video generation prompt: Two containers are placed side by side on a table. The left container contains a suitable amount of freshly made yogurt, while the right container contains an equivalent amount of yogurt that has continued fermenting for several additional days. pH paper is immersed into both containers to test the acidity and alkalinity.

Evaluation guide:
(i) Target concept: Progressive acidification during post-fermentation aging of yogurt.
Minimum mechanism: Lactic acid accumulation must be visually inferable via differential pH paper color response; aged yogurt must exhibit macroscopic physical evidence (whey separation + texture change) confirming extended fermentation time.
(ii)Storyline: Frame opens on static tabletop view → two identical containers enter frame already placed side-by-side → fresh yogurt fills left container (uniform white, no separation) → aged yogurt fills right container (immediately shows subtle whey pooling at surface) → pH paper approaches left container → full immersion and stable submersion → paper withdraws, revealing yellow-orange color → pH paper approaches right container → full immersion and stable submersion → paper withdraws, revealing orange-red color → final frame holds both papers side-by-side for direct hue comparison; entire sequence maintains fixed frontal viewpoint, no cuts, no zoom, no rotation; all actions occur within single continuous take.

Manual:
Experimental Procedure
1. Place two identical containers side-by-side on a flat table.
2. Fill the left container with freshly made yogurt; fill the right container with yogurt that has continued fermenting for several additional days (equivalent volume).
3. Dip one pH paper strip fully into the left container; hold for 1 second.
4. Dip another pH paper strip fully into the right container; hold for 1 second.
Observation of Experimental Phenomena
- Left pH paper turns yellow-orange (pH ~4.0–4.6); right pH paper turns orange-red (pH ~3.5–4.0).
- The aged yogurt shows visible whey separation and a denser curd structure compared with the fresh yogurt.
Summary of Experimental Principles
Lactic acid bacteria continue metabolizing lactose during aging, producing additional lactic acid → lowers pH → increases acidity → causes a greater color shift on pH paper toward the red end of the scale.

Prompt Grounding rubric:
level_1: No two containers visible; or only one container is present; or neither the fresh yogurt nor the aged yogurt is shown; or pH paper is absent; or the two containers are not placed next to each other on the table.
level_2: Two containers are present and placed on a table, but at least one of the following is missing: (a) the left container holds freshly made yogurt, (b) the right container holds yogurt that has continued fermenting for several additional days, (c) both amounts are visually matched in volume/level, (d) pH paper is present but never immersed in either container.
level_3: Two containers are placed next to each other on a table; the left container holds fresh yogurt, the right container holds yogurt aged several additional days; pH paper is immersed in both containers, either at the same time or one after the other; all objects (containers, both yogurt samples, pH paper) are visually identifiable and correctly assigned to their positions.
level_4: Everything described for the 3-point level holds, and in addition: the two containers are adjacent with no occlusion between them from the fixed viewpoint; the pH paper strip is visibly and fully submerged (not just resting on the surface or hovering above it) in each container; no extraneous objects interfere with viewing both containers together.
level_5: Everything described for the 4-point level holds, and in addition: the two containers stay adjacent on the table in the same relative positions from start to finish, without repositioning, shifting, or perspective drift, and both remain fully visible in frame throughout; each pH paper immersion is a single, deliberate, complete action with no hesitation, partial withdrawal, or misalignment.

Scientific and Causal Correctness rubric:
level_1: The pH paper shows the same color in both containers; or the color change contradicts the acidity trend (e.g., the right container's paper looks less acidic than the left's); or the fresh and aged yogurt look identical in texture and appearance; or neither pH paper strip changes color from its original hue after immersion.
level_2: The pH paper changes color in at least one container, but the color difference between left and right is missing, reversed, or inconsistent with the aged sample being more acidic (i.e., the right container's paper does not turn a distinctly deeper orange/red compared to the left's paler yellow/orange).
level_3: The pH paper shows two distinguishable colors: the left (fresh yogurt) container's paper turns a mildly acidic hue (roughly yellow-orange, pH ~4.0–4.6); the right (aged yogurt) container's paper turns a more acidic hue (roughly orange-red, pH ~3.5–4.0); the fresh yogurt looks uniform and white/opaque, while the aged yogurt shows at least one visible sign of continued fermentation (e.g., a thin layer of watery whey pooling on its surface), confirming the aging.
level_4: Everything described for the 3-point level holds, and in addition: the color contrast between the two paper strips is visually unambiguous and points the correct direction (the right strip is clearly more saturated toward red/deep-orange than the left); the aged yogurt shows at least one additional sign consistent with continued fermentation beyond whey pooling (e.g., a firmer or denser-looking curd, or visible surface dimpling) that the fresh yogurt does not show.
level_5: Everything described for the 4-point level holds, and in addition: the color difference is maximally clear (the right strip sits fully within the red-to-deep-orange range and the left strip fully within the yellow-to-light-orange range, with no in-between or ambiguous hue on either strip); the aged yogurt clearly shows both whey separation and a denser curd texture side by side with the fresh yogurt's uniform appearance, leaving no doubt about which sample is which.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal violation: one or both containers vanish and reappear in a different spot on the table; a pH paper strip appears already fully submerged in a container with no visible approach or entry motion; a container's position, size, or shape changes abruptly between frames; the yogurt inside a container is suddenly replaced by a different substance or color mid-shot; the lighting on the scene swings abruptly between bright and dark with no visible cause; or the tabletop/background changes color or texture between frames.
level_2: At least one major spatiotemporal violation: the two containers shift from sitting side by side to a different relative arrangement (e.g., one ends up in front of, behind, or overlapping the other); a pH paper strip's descent into a container skips visible frames so it appears to jump from hovering above the liquid straight to being fully submerged; the whey layer visible on the aged yogurt's surface appears and disappears between frames instead of remaining a stable surface feature once formed; or the shadows cast by the containers flip direction or intensity with no corresponding change in a light source.
level_3: Both containers stay in their original side-by-side positions on the table for the entire video, with no relative repositioning between them; each pH paper strip's motion is continuous from approaching its container, to entering the liquid, to sitting submerged; once visible, the whey layer on the aged yogurt's surface and the fill level in both containers stay in place rather than intermittently appearing or disappearing; neither container nor its contents distorts or breaks apart.
level_4: Everything described for the 3-point level holds, and in addition: each pH paper strip's descent into its container is smooth, without pausing mid-air, reversing direction, or jittering; the liquid surface in each container stays level and undisturbed apart from the small, physically expected ripple caused by the paper's entry; the table and containers show no unexplained sliding or vibration between frames.
level_5: Everything described for the 4-point level holds, and in addition: the timing of the two immersions is coherent (whichever container is dipped second follows the same smooth approach-and-entry pattern as the first, whether the two immersions happen one after the other or simultaneously); the paper tip, the surrounding liquid surface, and the container rims stay sharply defined and stable in every frame, with no warping, doubling, or blurring of these edges as the video plays.