Domain: Healthcare — Nutrition & Dietetics
Target concept: Browning of Apple Slices: A Comparison Between Lemon Juice (Ascorbic Acid) and Ordinary Air Exposure

Video generation prompt: Place freshly sliced apple pieces on two identical plates; pour lemon juice over the slices on the left plate, and leave the slices on the right plate untreated, then place both plates side by side.

Evaluation guide:
(i) Target concept: Enzymatic browning inhibition via ascorbic acid and acidification.
Minimum mechanism: Apple tissue must be freshly cut (exposing polyphenols and PPO enzyme to O₂); lemon juice must contact cut surfaces (delivering ascorbate + H⁺); untreated control must be identically exposed to ambient air; browning requires time but is visually detectable within seconds as initial discoloration onset.
(ii)Storyline: Frame 1–2: Two empty identical plates enter view and settle side-by-side. Frame 3–4: Fresh apple slices placed simultaneously on both plates in mirrored arrangement. Frame 5–6: Lemon juice poured *only* onto left-plate slices (liquid visibly wets surface). Frame 7–10: Static hold: right-plate slices show progressive brown edge development; left-plate slices remain uniformly un-browned; camera maintains fixed frontal viewpoint with full framing of both plates and unobstructed visibility of cut surfaces.

Manual:
Experimental Procedure
1. Place two identical white plates side-by-side on flat surface.
2. Arrange 4–6 freshly sliced apple pieces evenly on each plate.
3. Pour lemon juice over apple slices on left plate only.
4. Hold both plates motionless in frame for observation.
Observation of Experimental Phenomena
Within 10 seconds: apple slices on right plate develop visible brown discoloration on cut surfaces; apple slices on left plate retain original pale yellow/flesh color with no browning.
Summary of Experimental Principles
Lemon juice contains ascorbic acid and low pH, which inhibit polyphenol oxidase — the enzyme responsible for enzymatic browning in apples exposed to air.

Prompt Grounding rubric:
level_1: No apple slices are visible; the two plates are not both present; there is no lemon juice application shown at all; the two plates are never shown together in one shot; or there is no untreated plate present for comparison.
level_2: Both plates are present but are not shown together in the same shot; apple slices appear on only one of the two plates; lemon juice is present in frame but never poured onto the left plate; or the roles are reversed or unclear (e.g., juice poured onto the right plate, or it is unclear which plate went untreated).
level_3: Both identical plates sit together in a single fixed shot; fresh apple slices sit on both plates; lemon juice is visibly poured onto the left plate's slices; the right plate's slices have no liquid poured on them; which plate is treated and which is untreated is unambiguous from the camera's viewpoint.
level_4: Building on the 3-point description above: the poured lemon juice wets only the left plate's slices, with none landing on the right plate or the surrounding surface; the slices are cut and arranged comparably on both plates (similar count and size); no hand, bottle, or label blocks the view of either plate; the camera viewpoint stays fixed for the remainder of the clip.
level_5: Building on the 4-point description above: the lemon juice is poured onto the left plate's slices in the frame immediately following their placement, with no idle gap between placement and treatment; both plates stay fully inside the frame without cropping; the slices occupy a comparable visual area on each plate; once treatment is complete, no further drips, smears, or moving liquid disturb the still comparison.

Scientific and Causal Correctness rubric:
level_1: No color difference ever appears between the two plates (both stay pale, or both brown at the same rate); OR browning appears on the lemon-juice-treated slices instead of the untreated ones; OR a fruit other than apple is shown.
level_2: Apple slices are visible on both plates, but the browning pattern contradicts what lemon juice does, e.g., both plates brown fully within 10 seconds, the untreated plate stays pale while the treated plate browns, or both plates change color by the same amount with no visible contrast between them.
level_3: A visible contrast appears: the untreated slices on the right plate show brown discoloration on their cut surfaces, while the lemon-treated slices on the left plate keep their original pale yellow-cream color; neither plate shows an unrelated color shift such as green, blue, or black.
level_4: Building on the 3-point description above: the browning on the right plate stays confined to the exposed cut surfaces rather than spreading over the whole slice; the lemon juice leaves no artificial yellow tint or stain on the left plate's slices; the brown on the right plate reads as a typical tan-to-reddish-brown enzymatic color rather than gray or black; the left plate's slices show no sign of surface oxidation.
level_5: Building on the 4-point description above: the brown discoloration progresses radially outward from the cut edge on the right plate's slices only; the left plate's slices show no yellowing, darkening, or translucency change discernible at normal viewing scale from first frame to last; the contrast stays visually unbroken throughout (lemon juice on the left corresponds to an absence of browning there), with no competing phenomena (drying, wilting, pooled water) muddying the comparison.

Spatiotemporal Consistency rubric:
level_1: One of the two plates sits in a completely different spot from one frame to the next with nothing shown moving it, or a plate is simply absent from a frame where it should still be sitting; an apple slice changes position with no hand or pour motion moving it; the overall lighting swaps abruptly partway through, making the color comparison unreadable; either plate rotates or tips over; or the background changes between frames.
level_2: One plate visibly slides sideways between shots while the other stays put; an apple slice jitters in place or changes apparent size inconsistently frame to frame; the poured lemon juice appears as a static painted-on patch rather than liquid actually wetting the slices; or the shadow beneath one plate swaps to its opposite side with nothing in the scene explaining why.
level_3: Both plates stay visible in the same part of the frame throughout, with no plate swapped out, duplicated, or removed from view; both plates stay level and resting on the surface; the slices keep the same position and orientation on their respective plates from placement onward; the overall scene brightness stays even across both plates; no slice fragment floats free of its plate or breaks apart on its own.
level_4: Building on the 3-point description above: the lemon juice is shown as a continuous pour wetting the slices rather than cutting straight to an already-wet state; there is no flicker or strobing in the shot; neither plate nor slice warps or stretches out of shape; the shadow cast by the left plate at the moment the lemon juice is poured onto it falls on the same side as the shadow cast by the right plate in that same frame, and neither shifts sides by the time browning becomes visible on the right plate.
level_5: Building on the 4-point description above: the lemon juice pour follows a natural, gravity-driven arc rather than floating, reversing, or jumping mid-pour; the plates show no visible shake, stutter, or repeated frame from start to finish; the framing does not drift or zoom as if the camera had been bumped; both plate rims stay round and undistorted in every frame.