Domain: Engineering — Food and Bioprocess Engineering
Target concept: Casein in milk coagulates upon the addition of acid (lemon juice or vinegar).

Video generation prompt: Pour warm milk into a transparent glass bowl, and add lemon juice while gently stirring, then let it sit for a few minutes.

Evaluation guide:
(i) Target concept: Acid-induced coagulation of casein micelles in warm milk.
Minimum mechanism: Milk must be warm (to accelerate reaction kinetics but below denaturation threshold), contain native casein micelles, and be exposed to sufficient citric acid to lower pH below ~4.6; coagulation requires time in stillness for micelle aggregation to reach visible scale.
(ii)Storyline: [Phase 1: Setup] Transparent bowl enters frame containing warm milk (subtle surface sheen, no steam). [Phase 2: Intervention] Lemon juice visibly dispensed into milk while stirring utensil moves smoothly and continuously. [Phase 3: Transition] Stirring stops; utensil is fully withdrawn; bowl remains motionless. [Phase 4: Emergence] During stillness, small white aggregates appear and grow in number/size, exclusively within liquid volume, never at air-liquid interface or bowl wall. [Perspective constraint] Fixed frontal or slightly angled overhead view; entire bowl and upper 2/3 of liquid column must remain fully visible and unoccluded throughout all phases. [Visibility constraint] All critical events (juice entry, stir cessation, first aggregate appearance) must occur within the central 70% of frame and occupy ≥5% of frame area when visible.)

Manual:
Experimental Procedure
1. Pour warm milk into a transparent glass bowl.
2. Add lemon juice while gently stirring.
3. Let mixture sit undisturbed for a few minutes.
Observation of Experimental Phenomena
White curd-like aggregates form and become increasingly visible in the liquid during stillness; liquid remains white—no yellowing, browning, or layering.
Summary of Experimental Principles
Acid (citric acid in lemon juice) lowers pH, disrupting calcium bridges in casein micelles, causing them to coagulate into visible curds.

Prompt Grounding rubric:
level_1: No transparent bowl is visible; no milk is shown in it; there's no lemon juice or any container/source for it; no stirring motion of any kind occurs; the mixture is never shown sitting undisturbed.
level_2: A transparent bowl holds a liquid, but it isn't milk-like (e.g., it's water or stays fully clear); or the milk shown is at a temperature extreme that doesn't read as 'warm' (visibly icy with condensation fogging the bowl, or at a rolling boil); or lemon juice is never actually shown entering the bowl (only implied off-camera, with no visible stream or drop); or no stirring motion ever occurs.
level_3: A transparent bowl holds white milk that reads as warm, with no rolling boil, no condensation fogging the bowl, and no ice; lemon juice is visibly poured or squeezed into the milk; a utensil or finger stirs it gently; the bowl then sits undisturbed for long enough that a reaction could plausibly develop.
level_4: Everything in score 3 holds, and additionally: the lemon juice enters the milk while stirring is still happening (not strictly before or after it); the stirring stays smooth and gentle throughout (no vigorous whipping, scraping, or jerking); the bowl stays put in the frame the whole time; no unrelated object enters or leaves the shot; nothing is substituted in for milk (no pre-curdled liquid, no added solid clumps).
level_5: Everything in score 4 holds, and additionally: the lemon juice clearly comes from a recognizable source: a cut lemon wedge squeezed by hand, or a bottle clearly labeled as lemon juice; the stirring utensil or hand stays fully visible and is held the same way the whole time; the milk's surface shows a subtle warm sheen rather than condensation, ice crystals, or visible steam, consistent with mildly warm, not hot, cold, or boiling, milk.

Scientific and Causal Correctness rubric:
level_1: The milk stays completely smooth and liquid for the entire clip; no particles, flecks, or clumps ever appear; the milk's color and opacity never change (it stays plain white, with no yellow tinge and no watery separation).
level_2: The milk's appearance changes, but not the right way: it turns hazy or grainy without forming distinct particles, or its color shifts toward yellow or brown without any lemon juice having been added, or clumps appear before the lemon juice touches the milk, or only while stirring is still happening and never after the bowl goes still.
level_3: Once the bowl goes still, small white flecks or soft clumps become visible in the milk, clearly distinguishable from the surrounding liquid (not a blur or rendering glitch); the milk stays white with no yellow, green, or brown cast; once formed, the flecks or clumps don't dissolve back into the liquid; this clumping happens only after the lemon juice has been stirred in, never before.
level_4: Everything in score 3 holds, and additionally: the flecks or clumps grow in number and size the longer the bowl sits (they don't shrink or stop appearing partway through); they stay gently suspended or settle slowly, rather than shooting to the surface or sinking instantly; no separate watery layer forms beneath a clearer top layer; the surrounding liquid stays translucent-to-opaque white rather than turning clear or watery.
level_5: Everything in score 4 holds, and additionally: the flecks or clumps are white or off-white only, with no gray, yellow, or pink tint; they're spread through the visible milk rather than clumped into one or two isolated blobs; nothing that looks like a stray foreign speck or fiber gets mistaken for a curd; the clumps look soft, irregular, and loosely aggregated (like natural casein clumping), not like hard granules, crystals, or rubbery beads.

Spatiotemporal Consistency rubric:
level_1: The bowl's position or the milk's fill level jumps abruptly between shots with no visible cause; the lemon-juice stream seems to start from thin air, with no hand, lemon, or bottle visibly feeding it; the stirring utensil changes length or shape from one frame to the next; the scene's overall lighting shifts abruptly partway through (e.g., a sudden change in color temperature).
level_2: The bowl tilts or rotates by more than about 15 degrees with no visible hand or force causing it; the stirring motion skips ahead in jumps instead of flowing continuously; during the still phase, the bowl or milk surface trembles, drifts, or pans when nothing should be moving it; the shadow the bowl casts swings to a different direction between shots; the reflection on the bowl's surface doesn't match where the scene's light source appears to be.
level_3: The bowl stays upright and in the same spot the whole time; the milk's surface stays level and undisturbed once stirring stops; the lemon-juice stream stays visibly connected from its source down to the milk; the stirring motion flows smoothly with no missing steps; nothing blocks the view of the bowl during pouring, stirring, or the still phase; the shadow the bowl casts keeps roughly the same direction and softness across the whole clip.
level_4: Everything in score 3 holds, and additionally: the camera's framing (zoom, distance, angle) doesn't shift partway through; the stirring utensil in the foreground and the bowl in the background keep believable relative scale (no mismatched depth cues); the reflection on the bowl's surface stays steady and plausible, never flipped or warped; the stirring phase and the still phase both play out at a consistent pace, with neither one visibly sped up or slowed down relative to the other.
level_5: Everything in score 4 holds, and additionally: the utensil keeps the same size and orientation relative to the bowl throughout; moving edges (the utensil, the stirred milk surface) don't flicker, strobe, or leave duplicate/ghost trails; motion blur on the utensil matches its actual speed consistently (no sharp tip paired with a smeared handle); the bowl's rim and the milk's surface keep their true round/flat shape rather than bowing or warping.