Domain: Healthcare — Nutrition & Dietetics
Target concept: Emulsifying oil and water using lecithin or egg yolk

Video generation prompt: Place two identical transparent glasses side by side on a table. In the left glass, combine water and vegetable oil. In the right glass, combine water, vegetable oil, and a raw egg yolk. Stir each glass thoroughly, then let both glasses stand undisturbed.

Evaluation guide:
(i) Target concept: Lecithin-mediated emulsification of oil and water. Minimum mechanism: Egg yolk supplies lecithin, an amphiphilic phospholipid that adsorbs at the oil-water interface, lowering interfacial tension and coating dispersed oil droplets so they resist re-coalescing; without lecithin, oil and water are immiscible and the two liquids separate back into distinct layers once stirring stops, driven by density difference and interfacial tension alone. (ii) Storyline: [Phase 1: Setup] Two identical glasses enter frame side by side → left glass receives water then vegetable oil → right glass receives water, vegetable oil, and a raw egg yolk. [Phase 2: Action] Left glass is stirred, producing a swirling dispersion of oil droplets through the water → right glass is stirred, producing a similar swirling dispersion → stirring stops in both. [Phase 3: Observation] Both glasses are left standing → the left glass's droplets rise and coalesce, and the glass returns to two clear stacked layers (oil above water) within the observation window → the right glass's droplets remain suspended through the water column, keeping that mixture visibly cloudy without fully re-separating by the end of the clip. [Visibility constraints] Fixed frontal mid-shot; full glass height visible from base to rim; no occlusion of either glass; lighting is even enough to distinguish a clear layered liquid from a cloudy dispersed one; all phase transitions occur in continuous, uncut time.

Manual:
Experimental Procedure
1. Place two identical transparent glasses side by side.
2. Pour water and vegetable oil into the left glass.
3. Pour water, vegetable oil, and a raw egg yolk into the right glass.
4. Stir the left glass thoroughly; stir the right glass thoroughly.
5. Let both glasses stand undisturbed.
Observation of Experimental Phenomena
Left glass: the stirred oil-water mixture separates back into two clear stacked layers, oil on top of water, as the stirring-induced droplets rise and coalesce. Right glass: the stirred oil-water-yolk mixture stays visibly cloudy, with oil droplets remaining dispersed through the water rather than fully re-separating.
Summary of Experimental Principles
Egg yolk supplies lecithin, an amphiphilic emulsifier whose molecules position themselves at the surface of oil droplets suspended in the water, lowering interfacial tension and hindering droplet coalescence. This keeps small oil droplets dispersed in the water phase (a true oil-in-water emulsion) well after stirring ends. Without lecithin, the left glass's oil and water have no such stabilizer, so the two immiscible liquids re-separate by density difference soon after stirring stops.

Prompt Grounding rubric:
level_1: Fewer than two transparent glasses appear on screen; or water and vegetable oil are never both visible in the same establishing shot; or the right glass never receives a visibly added raw egg yolk; or the two glasses are arranged one behind the other instead of side by side; or neither glass is ever stirred.
level_2: Both glasses are present side by side and each contains water plus vegetable oil, but one of the following is true: the egg yolk is poured into the left glass instead of the right; or only one of the two glasses is ever stirred; or the clip ends immediately after stirring with no standing period shown for either glass.
level_3: Two identical transparent glasses stand side by side; the left glass holds only water and vegetable oil, the right glass holds water, vegetable oil, and a visibly added raw egg yolk; both glasses are stirred with visible swirling motion; afterward both glasses are shown standing undisturbed long enough to observe their post-stirring state.
level_4: Everything required for score 3 is present, and additionally: the two glasses match each other in height, width, and wall thickness; the egg yolk enters the right glass as a single intact yellow globule that visibly breaks apart once stirring begins (not already broken, powdered, or pre-diluted before stirring starts); each glass is stirred separately, one after the other, with the utensil rinsed or swapped between glasses rather than carried straight from one glass's liquid into the other; and once stirring ends in each glass, that glass is held steady in frame with no further jostling or re-entry of the utensil.
level_5: Everything required for score 4 is present, and additionally: both glasses rest on the same tabletop plane at the same distance from the camera with nothing placed between them; the egg yolk is added to the right glass only after its water and oil are already poured in, never before; stirring is completed in one glass before stirring begins in the other; and after stirring stops, the camera keeps showing both glasses standing undisturbed for a clearly extended period rather than cutting away immediately, giving enough time on screen for any settling behavior to be observed.

Scientific and Causal Correctness rubric:
level_1: The right glass (water + oil + egg yolk) separates into two clear stacked layers just as fast as the left glass (water + oil only), showing no effect of the yolk at all; or the left glass (water + oil only) stays cloudy indefinitely as if it also held an emulsifier; or oil and water appear to fully dissolve into one clear liquid in either glass.
level_2: The left glass's water and oil layers reform after stirring, and the right glass stays cloudier or slower to clear than the left, but only marginally so (e.g., the right glass clears within a few seconds of the left rather than remaining visibly cloudy for a clearly longer stretch), so the yolk's emulsifying effect is barely distinguishable from the plain oil-water control.
level_3: After stirring and standing, the left glass (water + oil only) returns to two clear stacked layers with a visible oil-water boundary within a short time; the right glass (water + oil + egg yolk) stays visibly cloudy or milky, with oil droplets still dispersed through the water, for noticeably longer than the left glass takes to clear, showing the yolk measurably slows or prevents re-separation.
level_4: Everything required for score 3 is present, and additionally: the left glass's cleared water shows no leftover haze or droplets once its layers reform; the right glass's cloudiness is spread through the water column rather than confined to a thin band, consistent with oil droplets carried throughout the water rather than only floating at the surface; and neither glass shows an unexplained clearing-then-reclouding cycle during the standing period.
level_5: Everything required for score 4 is present, and the contrast between the two glasses is unmistakable and holds for the entire standing period shown: the left glass is fully clear with a sharp, flat oil-water interface; the right glass remains an evenly cloudy oil-in-water dispersion with no sharp re-separation line forming, consistent with lecithin from the egg yolk coating the dispersed oil droplets and keeping them suspended in the water rather than letting them coalesce and rise.

Spatiotemporal Consistency rubric:
level_1: The right glass swaps position with the left glass partway through the clip, so the egg-yolk mixture ends up on the side where plain water and oil started; or the stirring utensil passes straight through a glass wall instead of dipping in from the open top; or the liquid inside a glass jumps from fully mixed to fully layered (or the reverse) between two consecutive frames with no stirring or settling motion shown in between; or a glass that was on screen is absent for part of the clip and then present again later with no camera move to account for it; or the whole shot's lighting swings abruptly between bright and dark with no lamp, flame, or other light source change visible to explain it.
level_2: Both glasses stay on screen throughout, but one of them slides sideways or drifts up/down on the table between the stirring phase and the standing phase; or the stirring swirl abruptly changes speed or direction as if frames were skipped; or the bright reflection on the front of a glass jumps to a different spot right when stirring starts or stops, with no matching change in the room's light source.
level_3: The left and right glasses each stay in their own spot on the table from the first stirring shot through the final settled shot; the stirring utensil enters and exits each glass's liquid smoothly, without cutting through the glass wall or freezing mid-swirl; the oil-water boundary forming in the left glass and the cloudy region in the right glass move and settle in a physically continuous way, with no liquid level jumping up or down apart from what stirring or pouring would cause.
level_4: Everything required for score 3 is present, and additionally: the camera holds one fixed framing for the whole clip, with no pan, tilt, or zoom; the tabletop and any background objects stay put and unchanged behind the two glasses; the curved meniscus at the top of each liquid and the rim of each glass keep the same shape and position relative to the glass across the stirring and standing shots; and the stirring utensil's path through each glass follows one smooth arc rather than reversing direction or pausing unnaturally partway through.
level_5: Everything required for score 4 is present, and additionally: the swirling and settling motion in both glasses reads as smooth throughout, with no stuttering, motion blur that mismatches how fast the liquid is actually moving, or repeated frames; the glass walls keep a consistent, believable refraction of what's behind them as the liquid inside goes from swirling to settled; and the left and right glasses keep the same spacing and alignment relative to each other and to the camera for the entire clip, with no shift in their apparent distance as the camera's implied viewpoint stays fixed.