Domain: Engineering — Food and Bioprocess Engineering
Target concept: Vitamin B12 Determination (Cyanocobalamin Colorimetric Method)

Video generation prompt: Take 2 mL of pig liver extract into a test tube, add 1 drop of potassium cyanide solution and 2 drops of p-dimethylaminobenzaldehyde reagent.

Evaluation guide:
(i) Target concept: Visual verification of the cyanocobalamin-specific color development sequence in the vitamin B12 determination assay: potassium cyanide (KCN) converts native cobalamins in pig liver extract into cyanocobalamin and supplies the acidity the reaction needs, and only the subsequently added p-dimethylaminobenzaldehyde (p-DMAB) reagent reacts with that cyanocobalamin to produce the visible reddish-pink color.
Minimum mechanism: Pig liver extract must contain native cobalamin forms; the KCN drop must disperse fully into the extract, exchanging cyanide onto the cobalt center to form cyanocobalamin and providing the acidic conditions the subsequent reaction needs, but this conversion alone produces no visible color change; the two p-DMAB drops that follow condense specifically with the cyanocobalamin's corrin ring under those acidic conditions to generate the reddish-pink chromophore, so the color appears only once the p-DMAB addition is complete.
(ii) Storyline: [Frame 0-2] Static shot of an upright test tube holding 2 mL of dark red-brown pig liver extract. [Frame 3-4] The KCN dropper enters frame, positions at the tube mouth, and releases exactly 1 fully formed drop that detaches and enters the liquid, dispersing without any visible color change. [Frame 5-6] The KCN dropper withdraws; the p-DMAB dropper enters, positions identically, and releases exactly 2 discrete drops in sequence (the first fully enters, then the second forms and enters). [Frame 7-10] Reddish-pink color emerges only after the second p-DMAB drop completes its entry, initiating at the impact site and expanding to fill the liquid volume; no color appears earlier, elsewhere, or in an incorrect hue. All action is shown from a fixed frontal close-up with unobstructed view of the tube interior, droplet trajectories, and liquid surface.

Manual:
Experimental Procedure
1. Place 2 mL pig liver extract into a clean test tube.
2. Add 1 drop of potassium cyanide solution using a dropper.
3. Add 2 drops of p-dimethylaminobenzaldehyde reagent using a separate dropper.
Observation of Experimental Phenomena
The KCN drop disperses into the extract without producing any visible color change. A distinct reddish-pink color develops only once the two p-DMAB drops have been added, beginning at the site of p-DMAB entry and spreading uniformly through the liquid.
Summary of Experimental Principles
Potassium cyanide exchanges its cyanide ion onto the cobalt center of the cobalamin forms present in liver extract, converting them into cyanocobalamin and supplying the acidic conditions the reaction needs; this conversion by itself produces no visible color. p-Dimethylaminobenzaldehyde then reacts specifically with the cyanocobalamin's corrin ring under these acidic conditions to form a reddish-pink chromophore — the color-forming step of the assay.

Prompt Grounding rubric:
level_1: No test tube is present; no pig liver extract is visible; neither the potassium cyanide dropper nor the p-dimethylaminobenzaldehyde reagent bottle is shown; no liquid-transfer action occurs; there is no indication of the 2 mL volume or of any 1-drop/2-drop dispensing.
level_2: A test tube containing liquid is present, but the liquid is not identifiable as pig liver extract; at least one reagent container (e.g., a dropper bottle) appears, but no dispensing action occurs; no countable drops of either reagent are dispensed; no order of addition is shown.
level_3: A test tube holds a dark red-brown opaque liquid consistent with pig liver extract; both the KCN dropper and the p-DMAB dropper appear; exactly 1 drop of KCN and then 2 drops of p-DMAB are dispensed into the tube in that order; the test tube and both droppers stay within the same frame throughout.
level_4: Everything described for score 3 holds, and in addition: each dropper tip visibly contacts the tube mouth or interior while dispensing (no drops released in mid-air away from the tube); every drop is fully formed and detaches from its tip before entering the liquid; no extraneous object (glove, label, timer) blocks the core elements; the tube stays upright and stationary; the whole dispensing sequence plays out in one continuous shot with no cut.
level_5: Everything described for score 4 holds, and in addition: each of the three drops is individually distinguishable rather than merged or blurred together; the KCN drop fully enters and disperses into the liquid before the p-DMAB dropper enters frame; the two p-DMAB drops are dispensed only after the KCN drop has mixed in; no reflection glare, motion blur, or lens flare obscures any drop's formation, fall, or entry; the camera holds a fixed frontal close-up showing the full tube height and the alignment of each dropper tip with the tube mouth.

Scientific and Causal Correctness rubric:
level_1: No reddish-pink color ever appears: the liquid stays dark red-brown, or shifts to an unrelated hue such as yellow, blue, or green; OR the KCN and p-DMAB drops are added in the wrong order or at the same time, so no clean cause can be tied to p-DMAB.
level_2: A color shift toward pink or red happens, but begins before the p-DMAB drops have finished entering (either right after the KCN drop alone or partway through the p-DMAB addition) rather than only once both p-DMAB drops are in; or the resulting hue is a mismatch such as orange, purple, or gray rather than reddish-pink.
level_3: The KCN drop disperses into the pig liver extract without producing any visible color change; only once the two p-DMAB drops that follow have fully entered does a reddish-pink color appear in the liquid.
level_4: Everything described for score 3 holds, and in addition: the reddish-pink color stays confined to the liquid itself rather than tinting the tube wall or a droplet's surface; the liquid remains visually homogeneous with no precipitate, cloudiness, or layering; the color does not begin to appear until the second p-DMAB drop has fully entered.
level_5: Everything described for score 4 holds, and in addition: the reddish-pink emerges smoothly once the p-DMAB drops complete their entry, with no pulsing, flashing, or flickering; by the final frame the reddish-pink fills the whole liquid volume with no leftover patch of the original dark red-brown or any other color; no visible trace of color appears during or immediately after the KCN drop, before the p-DMAB drops arrive.

Spatiotemporal Consistency rubric:
level_1: Between one frame and the next, the test tube jumps to a different spot in frame, or the liver-extract fill level changes abruptly with no pouring motion shown; a dropper appears already touching the tube mouth with no approach shown beforehand; the lighting suddenly brightens, darkens, or flickers between frames with no light source or camera change to explain it; OR the tube topples or tilts on its own with no hand, clamp, or stand shown causing it.
level_2: The tube stays on screen but visibly slides sideways or bobs up and down between the KCN step and the p-DMAB step; a dropper's tip separates from the tube mouth mid-release so its drop appears to hang in open air; the liquid sits perfectly still right up until a drop lands, then erupts into a splash far larger than one drop could cause.
level_3: The test tube stays upright and rooted to the same spot in frame for the whole clip; the KCN dropper, and later the p-DMAB dropper, each travel down a visible, continuous path to the tube mouth before releasing a drop; the liquid dips and smooths back out gently each time a drop lands, rather than freezing mid-splash or vanishing into the liquid instantly.
level_4: Everything described for score 3 holds, and in addition: the glass test tube shows no warping, stretching, or squeezing of its outline as either dropper moves past it; the shadow the KCN dropper casts on the tube while approaching and releasing its drop falls on the same side as the shadow the p-DMAB dropper casts during its own approach and release moments later, rather than the two droppers' shadows seeming to come from different directions; the tube's transparency and wall thickness look the same in the last frame as in the first.
level_5: Everything described for score 4 holds, and in addition: each drop falls with a natural, accelerating descent rather than drifting at constant speed or floating; the ripple the liquid makes after each drop lands visibly settles back to a flat surface within a couple of seconds rather than persisting or growing; the clip shows no stutter, repeated frame, or misaligned jump in the position of the tube, either dropper, or the liquid surface from start to finish.