Domain: Healthcare — Nutrition & Dietetics
Target concept: Melamine Detection (Picric Acid Colorimetric Method)

Video generation prompt: Place the liquid milk sample into a test tube, and add the picric acid reagent using a pipette. Gently shake to mix thoroughly and allow it to stand for a period of time to complete the reaction. Use standard laboratory glassware to clearly demonstrate the procedure of handling test tubes and adding reagents in the correct order.

Evaluation guide:
(i) Target concept: Visual confirmation of melamine detection via formation of a spatially segregated, color-distinct precipitate-solution biphasic system following standardized reagent addition and settling.
Minimum mechanism: Picric acid must be amber-colored in solution; milk must remain liquid-phase prior to addition; precipitation requires time-dependent molecular aggregation with gravity-driven sedimentation; interface formation necessitates immiscibility and density differential.
(ii)Storyline: [Phase 1: Setup] Test tube centered, empty → milk dispensed into it (visible meniscus rise). [Phase 2: Addition] Pipette approaches vertically, tip breaches tube opening → amber reagent flows in as discrete drops → meniscus rises again. [Phase 3: Mixing] Hand rotates test tube slowly in closed-loop circular path → liquid swirls with coherent vortex → surface deforms uniformly. [Phase 4: Standing] Tube placed upright → swirling stops → meniscus oscillates and dampens → surface flattens → yellow particles descend and accumulate at base → sharp horizontal interface emerges between clear supernatant and dense precipitate layer. All phases viewed from fixed frontal angle with full test tube in frame; no cutaways, no POV shifts, no zooms.

Manual:
Experimental Procedure
1. Place 2 mL liquid milk sample into clean test tube using graduated cylinder.
2. Add 1 mL picric acid reagent using calibrated glass pipette — tip must enter tube opening.
3. Gently shake test tube in circular motion for 5 seconds, then place upright and allow to stand undisturbed for 60 seconds.
Observation of Experimental Phenomena
A compact, fine-grained yellow precipitate forms at the bottom of the test tube; clear amber-yellow supernatant remains above.
Summary of Experimental Principles
Melamine reacts with picric acid under acidic conditions to form an insoluble yellow melamine-picrate complex — the presence of this precipitate confirms melamine contamination.

Prompt Grounding rubric:
level_1: No test tube appears; no liquid milk sample is shown; no picric acid reagent bottle or pipette appears; none of placing milk, adding reagent, or shaking is shown.
level_2: At least one required item appears (test tube, pipette, or milk), but the three key actions (placing milk in the tube, adding picric acid by pipette, and gently shaking) do not happen in that order; or an item is swapped for something else (e.g., a plain eyedropper instead of a graduated pipette), or the pipette tip never actually reaches the tube's opening.
level_3: The test tube, milk sample, and picric acid reagent (in a labeled bottle) are all shown; the pipette is used to deliver the reagent into the tube; milk is placed in the tube before the reagent is added; a gentle shaking motion follows the addition. The three actions happen in the right order, but a container is unlabeled, or the shaking is missing, jerky, or too rough, or the standing period is not shown as a period of stillness.
level_4: All items are present and clearly identifiable: a clear test tube, opaque white milk, amber picric acid solution in a labeled bottle, and a glass pipette with a bulb; milk goes in first, then picric acid is added with the pipette tip entering the tube opening, then a gentle circular shaking motion follows, then a period of visible stillness represents the standing time; nothing is swapped, mislabeled, or shown out of order.
level_5: Everything in the 4-point description holds, plus the pipette releases the reagent as visible, controlled drops with no splashing or bubbles forced out; the shaking keeps a steady rhythm and size without sudden jerks or pauses; the stillness phase shows the tube and liquid surface completely at rest; and the whole sequence is shown from one steady frontal angle with the full tube height and the pipette tip inside the tube visible during addition.

Scientific and Causal Correctness rubric:
level_1: No color change happens at all: the liquid stays uniformly white the whole time; no precipitate or layered interface ever forms; or the picric acid reagent itself looks colorless, blue, or green instead of amber, contradicting what picric acid actually looks like.
level_2: The picric acid reagent is present but the wrong color (e.g., red, purple, or deep orange instead of amber); or the milk looks solid or gel-like instead of a liquid; or no mixing ever visibly happens; or the yellow color appears the instant the reagent touches the milk rather than after some delay for reaction and settling.
level_3: Amber picric acid is added to the white milk, gentle shaking occurs, and after standing, a distinct yellow precipitate settles at the bottom of the tube; the color and location are right, but the precipitate looks clumpy or forms unevenly on one side rather than spread across the whole bottom, or the liquid above stays cloudy instead of turning at least somewhat clear.
level_4: The sequence matches what's expected: amber reagent stirred into milk gives a uniform yellow-tinted mixture, then after standing, a clearer liquid layer sits above a compact, fine-grained yellow precipitate filling roughly the bottom third of the tube; there are no stray floating particles, no persistent haze in the upper liquid, and no shift to an orange or brown color that would suggest something went wrong.
level_5: Everything in the 4-point description holds, plus the precipitate visibly forms only after the shaking stops, settles into a fairly sharp, level boundary with the liquid above, is evenly packed across the bottom of the tube, and the liquid above the precipitate looks essentially clear, matching how a yellow melamine-picrate precipitate should look once it has settled.

Spatiotemporal Consistency rubric:
level_1: The test tube's position or appearance resets between frames instead of moving continuously; the pipette jumps from the hand straight to the tube with no travel path shown; the liquid's level or shape changes suddenly between frames instead of smoothly; the lighting flips abruptly, such as a shadow vanishing then reappearing with no cause.
level_2: Continuity breaks in a smaller way: the pipette tip is shown entering the tube but the tube's wall is missing from that same frame; the shaking hand's position resets mid-motion instead of moving continuously; or during the standing period something moves that shouldn't, such as the table appearing to shake or the camera visibly drifting.
level_3: The pipette stays next to the tube throughout the addition step; the test tube stays centered in frame during both the shaking and standing phases; the liquid surface moves smoothly while shaking and settles down gradually afterward; the tube's shape doesn't bend or distort, and the lighting doesn't flicker.
level_4: Everything in the 3-point description holds, plus the pipette's approach into the tube opening is a straight downward motion rather than tilted sideways; the shaking follows a smooth, small circular path without sudden changes in direction; and during standing, the ripples on the liquid surface visibly settle down and flatten out over time rather than stopping instantly or bouncing back up.
level_5: Everything in the 4-point description holds, plus the whole clip plays out with no visible skips: the pipette tip stays touching or inside the tube's opening throughout the addition rather than appearing to hover apart from it, the tube's base stays planted in the same spot on the surface for the whole procedure, and the lighting and shadow pattern on the tube and liquid stay the same from milk placement through the final standing period.