Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Detection of Acesulfame K

Video generation prompt: A 10 mL food extract containing acesulfame potassium was placed in a test tube. Potassium ferricyanide solution was added and briefly mixed to allow any reducing substance in the extract to react. A ferric chloride solution was then added, the mixture was thoroughly shaken, and continuous images were captured with the camera aligned with the test tube.

Evaluation guide:
(i) Target concept: Visual confirmation of Prussian blue formation as a qualitative indicator that a reducing substance (here, acesulfame K) is present in the food extract, converting some of the added ferricyanide into ferrocyanide before a ferric salt is introduced to react with it.
Minimum mechanism: Potassium ferricyanide must first be mixed with the extract long enough for any reducing capability in the sample to convert some of it into ferrocyanide; a ferric chloride solution must then be added so its Fe³⁺ ions react with that newly formed ferrocyanide; mechanical agitation drives the collision-based reaction; the product is an insoluble blue colloidal precipitate (not a dye or complex in solution), and it can only appear because the first reagent was partly reduced before the ferric salt arrived.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube containing colorless food extract. [Frame 3–5] First reagent (amber potassium ferricyanide) added: droplets enter frame from top, contact the surface, sink, and the tube is briefly agitated to mix. [Frame 6–8] Second reagent (pale yellow ferric chloride) added identically. [Frame 9–12] Tube grasped and shaken: oscillatory motion visible, liquid sloshes with coherent meniscus deformation. [Frame 13–end] Tube held still: blue particles nucleate and disperse continuously; no settling, no dissolution, no color fade. Perspective: Fixed frontal view aligned to the tube's central axis; the entire tube length and liquid column are fully visible at all times; no occlusion by hands after shaking ends.

Manual:
Experimental Procedure
1. Place 10 mL food extract into a clean, clear glass test tube.
2. Add potassium ferricyanide solution dropwise and briefly agitate to mix.
3. Add ferric chloride solution dropwise.
4. Cap and shake the tube vigorously for 3 seconds.
5. Hold the tube steady and capture continuous images aligned with the tube's axis.
Observation of Experimental Phenomena
Blue granular precipitate (Prussian blue) forms throughout the liquid phase after the ferric chloride is added and the tube is shaken; no color change occurs before this point; the precipitate remains suspended rather than settling.
Summary of Experimental Principles
Acesulfame K detection relies on it acting as a reducing agent: once mixed with potassium ferricyanide, it reduces some of the ferricyanide to ferrocyanide. When ferric chloride is then added, its Fe³⁺ ions react with this newly formed ferrocyanide to form insoluble Prussian blue (Fe₄[Fe(CN)₆]₃). Because the ferrocyanide is only generated if a reducing substance was present in the extract, the appearance of Prussian blue after the ferric chloride is added indicates the presence of a reducing analyte such as acesulfame K in the sample.

Prompt Grounding rubric:
level_1: No test tube is present; no food extract is visible; neither the potassium ferricyanide nor the ferric chloride solution is ever shown being added; there is no fixed camera view of an upright test tube; or none of the three core actions (placing the extract, adding the two reagents in order, shaking) is depicted.
level_2: A single cylindrical transparent container appears, but it is not identifiable as a test tube; liquid is visible inside, but there is no evidence of two distinct reagent additions (ferricyanide, then ferric chloride); no shaking motion is shown; or the camera viewpoint is unstable or oblique rather than aligned with the tube's axis.
level_3: A standard clear glass test tube stands vertically, holding a visible volume of colorless liquid consistent with the food extract; two separate dropper-based additions occur in order: first an amber potassium ferricyanide solution, then a pale yellow ferric chloride solution; the tube is then shaken by hand with visible oscillatory motion; the camera stays fixed and aligned with the tube's long axis throughout.
level_4: Everything required at the 3-point level holds. In addition, both reagent solutions keep a consistent, distinguishable color (amber versus pale yellow) across frames; the shaking motion is continuous and moves along the full length of the tube; the test tube stays completely in frame without cropping; and no extraneous objects (gloves, labels, background text) block or misrepresent the setup.
level_5: Everything required at the 4-point level holds. In addition, the reagent order is unambiguous (ferricyanide first, then ferric chloride); shaking begins right after the second addition and continues without pause until the clip ends; the liquid's meniscus stays intact during both additions with no overflow or spill; the tube's outer wall shows no condensation, smudges, or reflections that obscure the liquid inside; and the camera stays perfectly coaxial with the tube's axis with constant framing throughout.

Scientific and Causal Correctness rubric:
level_1: No color change occurs and the liquid stays colorless throughout; no precipitate or turbidity ever forms; there is no visible reaction interface; or the reagents are shown with identical or implausible colors (e.g. both colorless, or already blue before mixing).
level_2: A single uniform color shift occurs (e.g. the whole solution turns green), which does not match Prussian blue's granular blue appearance; a precipitate appears before both the ferricyanide and the ferric chloride have been added and mixed; or a color change happens before any reagent is added.
level_3: After the ferric chloride is added and the tube is shaken, localized blue particles or a faint blue cloudiness appear and gradually increase; the blue color stays confined to the liquid, with no blue coating forming on the tube walls; the color change follows the correct order: ferricyanide added and mixed first, then ferric chloride added, then shaking, then the onset of blue particles.
level_4: Everything required at the 3-point level holds. In addition, the blue coloration looks granular and uneven, consistent with a colloidal Prussian blue precipitate, rather than a smooth, uniform dye-like tint; no red, brown, or orange hues appear (which would suggest iron hydroxide forming instead); the blue particles stay suspended during the observation window rather than settling quickly; and there is no gas bubbling or heat-shimmer effect.
level_5: Everything required at the 4-point level holds. In addition, the blue precipitate appears only after the ferric chloride has been added and the tube has been shaken, not right after the ferricyanide addition alone; the particles look fine and evenly dispersed, with no visible clumps larger than about 1 mm, rather than clumped into large visible chunks; the blue intensity keeps increasing steadily across the frames after shaking, without fading or bleaching; and there is no competing visual effect (light flare, chromatic fringing) that could be mistaken for the blue color.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from one or more frames and then reappears in the same spot with no motion connecting its absence to its return; the liquid inside changes level abruptly between frames with no pouring, draining, or spilling shown to explain it; a reagent droplet appears in mid-air without ever leaving the dropper tip; the shaking motion starts or stops with no acceleration or deceleration at all; or the camera jerks or rotates abruptly mid-clip.
level_2: The tube stays visible but shifts sideways or rotates more than about 15 degrees with no physical cause; the liquid's meniscus oscillates in a way that looks too fast and undamped to be plausible; a reagent addition appears to begin before its dropper enters the frame; or the shaking motion has a gap of several frames where it visibly pauses mid-motion.
level_3: The test tube stays fixed in position and orientation throughout; the liquid surface deforms plausibly while being shaken (the meniscus rises and falls smoothly, without shearing or tearing); the reagent droplets detach from the dropper tip and travel downward along a continuous path before entering the liquid; and the shaking motion is rhythmic and sustained, with a sense of physical inertia in how the tube moves.
level_4: Everything required at the 3-point level holds. In addition, there is no mismatch between how the tube's base and the background move relative to each other; the lighting and shadow on the tube's surface do not flicker or jump between frames; each droplet's impact produces a brief ripple on the liquid surface that spreads outward and settles naturally; and the tube itself never visibly flexes, bends, or compresses under the hand's grip.
level_5: Everything required at the 4-point level holds. In addition, the specular highlight on the tube's glass stays in a consistent position and brightness across all frames; the liquid surface keeps a coherent, continuously changing refraction of what's behind it as it moves; no motion blur hides the droplets' paths or the precipitate forming; and every frame is distinct and in the correct temporal order, with none repeated or out of sequence.