Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Ochratoxin Detection

Video generation prompt: Ten milliliters of a grain extract containing ochratoxin were placed in a test tube, followed by the addition of p-nitroaniline-sodium hydroxide solution. The mixture was thoroughly shaken and allowed to stand.

Evaluation guide:
(i) Target concept: Visual colorimetric detection of ochratoxin A via azo-coupling with a pre-diazotized p-nitroaniline reagent under alkaline conditions.
Minimum mechanism: The p-nitroaniline reagent used here is supplied in its pre-diazotized form (diazotized beforehand with nitrite under acid, then buffered into the alkaline sodium hydroxide solution added in this step); in alkaline medium its diazonium group undergoes azo-coupling with ochratoxin A to yield a conjugated azo chromophore absorbing in the visible range (~420–460 nm), producing a yellow-orange hue; the color must emerge only after mixing and standing, not during addition or shaking.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube containing pale yellow transparent grain extract (10 mL volume implied by fill level). [Frame 3–4] Reagent bottle/dropper enters frame from right, dispenses yellow-brown p-nitroaniline-NaOH solution into tube; liquid streams visibly into extract, forming temporary stratified layers. [Frame 5–7] Hand grasps tube and performs ≥3 full oscillatory shakes; liquid sloshes with inertia, meniscus deforms dynamically. [Frame 8–10] Hand releases; tube stands motionless; stratified layers disappear; uniform yellow-orange color emerges and stabilizes across entire column while maintaining full transparency and concave meniscus. All events occur from fixed frontal viewpoint with consistent lighting and no cuts.

Manual:
Experimental Procedure
1. Place 10 mL grain extract into a clean test tube.
2. Add p-nitroaniline-sodium hydroxide solution to the tube.
3. Shake tube vigorously and uniformly.
4. Let tube stand undisturbed.
Observation of Experimental Phenomena
A uniform yellow-orange color develops in the liquid after standing — indicating ochratoxin presence.
Summary of Experimental Principles
The p-nitroaniline reagent used in this assay is supplied pre-diazotized; under the alkaline conditions of the added solution, its diazonium group couples with ochratoxin A to form a stable yellow-orange azo dye, enabling visual colorimetric detection in grain samples.

Prompt Grounding rubric:
level_1: No test tube is shown, no grain extract is visible, no p-nitroaniline–sodium hydroxide solution appears, no shaking action is depicted, and no standing/still phase is shown.
level_2: At least one correct object is present (the test tube, the grain extract, or the reagent bottle), but none of the four actions (placing extract in the tube, adding the reagent, shaking, and letting it stand) happen in sequence; objects appear unrelated or mislabeled (e.g., a container labeled 'water' instead of grain extract), or the order contradicts the prompt (e.g., the reagent is added before the extract).
level_3: The test tube holds a clear liquid consistent with grain extract, the p-nitroaniline–sodium hydroxide solution is visibly poured in, shaking occurs, and stillness follows (all four steps appear in the right order), but at least one object is mislabeled or the wrong color/type (e.g., the reagent looks blue instead of yellow-brown, or the extract looks opaque white instead of pale yellow), or the hand enters from an inconsistent side across steps.
level_4: All four objects (the test tube, the grain extract, the p-nitroaniline–sodium hydroxide reagent, and the hand performing the actions) appear correctly typed and in the right order: extract already in the tube, reagent poured in, tube shaken, then left standing; no object is mislabeled or swapped for a different vessel (e.g., no beaker replacing the test tube), the camera viewpoint stays fixed, and no object or hand jumps position between shots; a brief motion blur during the shake or a glare reflection on the glass is still acceptable at this level.
level_5: The test tube is a clear cylindrical glass vessel; the grain extract is a pale yellow, transparent liquid filling it to a level consistent with about ten milliliters; the p-nitroaniline–sodium hydroxide reagent is a visibly distinct yellow-brown liquid dispensed from a labeled dropper or burette directly into the tube; the shaking is continuous and vigorous without interruption, and the following stillness clearly lasts longer than the shake itself; the tube, extract, and reagent stay in consistent relative position except for the depicted pouring and shaking motion, and there is no lighting jump, no glass deformation, and no flicker in the image from one frame to the next.

Scientific and Causal Correctness rubric:
level_1: No color develops in the tube at any stage (the liquid still looks like plain pale-yellow extract after standing, with no yellow-orange hue emerging), or the tube shows an immediate precipitate with no accompanying color shift, so there's no visible link between adding the reagent, shaking, and any resulting color.
level_2: A color does appear, but it's the wrong one for this assay (blue, green, red, or black rather than yellow-orange), or it appears before the reagent is added or before shaking is complete, or the final hue matches neither a positive (yellow-orange) nor a negative (pale yellow) result.
level_3: The yellow-brown reagent mixes into the pale-yellow extract, the tube is shaken, and the liquid ends up a uniform yellow-orange, matching a positive ochratoxin reaction, but the color either finishes forming before the shaking ends, develops visibly during the shaking itself rather than during the later standing period, or the liquid turns cloudy or develops a precipitate instead of staying a clear, homogeneous solution.
level_4: The uniform yellow-orange color appears only after shaking has stopped and while the tube stands undisturbed, with no cloudiness, no layering, and no color already visible during the shake; the hue is even from top to bottom of the column and stabilizes within roughly the first half of the standing period, consistent with the expected coupling reaction between ochratoxin A and the pre-diazotized p-nitroaniline reagent.
level_5: The final color is perfectly even across the whole liquid column, with no streaking, gradient, or visible interface; the solution stays completely clear with no haze or particles; the yellow-orange result is clearly distinguishable both from the original pale-yellow extract and from the transient stratified layering seen right after the reagent is poured in but before shaking; and the color is absent throughout shaking, fully present partway through standing, and unchanged for the remainder of the clip.

Spatiotemporal Consistency rubric:
level_1: The liquid level in the tube changes abruptly between shots with no visible pouring motion connecting them, the shaking motion skips between impossible positions, the lighting swings from bright to dark between consecutive frames with no cause, the tube itself appears to bend or warp, or the background flickers in and out.
level_2: A hand carrying the reagent enters the frame and then disappears before actually adding it, the shaking begins mid-motion with no build-up, the tube goes still before the shaking motion has actually stopped, the curve of the liquid surface looks different from one frame to the next with no consistent cause, or a reflection or highlight on the glass jumps position even though neither the camera nor the light source moved.
level_3: The pour into the tube looks like a controlled, continuous stream; the shaking shows a natural back-and-forth rhythm that gradually settles; the tube then goes completely still; the liquid surface settles smoothly rather than jumping; and the tube's size and orientation stay constant throughout, though one frame may show a brief double-exposure look on the hand during the shake, or the liquid surface may show a short-lived, physically odd ripple.
level_4: The pour shows unbroken flow from the reagent container into the tube; the shaking's oscillation decays naturally rather than stopping abruptly; the tube shows no residual wobble once still; the liquid surface moves from turbulent to rippling to flat without any sudden jump; reflections and highlights track consistently with the implied camera and light position; and the tube shows no warping, flipping, or clipping; a single frame of mild motion blur that doesn't obscure what's happening is still acceptable.
level_5: There is no motion blur beyond what the depicted speed would naturally produce; the tube, liquid surface, and background stay aligned frame to frame with no perspective mismatch; the liquid's turbulence during shaking and its settling afterward look like real fluid behavior with no unnatural overshoot or bounce; the lighting stays steady with no sudden change in brightness or a highlight that jumps position; and the camera framing holds rock-steady with no drift throughout the entire sequence.