Domain: Engineering — Food and Bioprocess Engineering
Target concept: Chocolate blocks soften and liquefy upon mild heating.

Video generation prompt: A piece of chocolate is placed on a slightly heated metal pan, and it is continuously recorded for several minutes while being heated.

Evaluation guide:
(i) Target concept: Solid-to-liquid phase transition in a heterogeneous food matrix driven by conductive heating from below.
Minimum mechanism: Chocolate must be in direct physical contact with a thermally conductive surface maintained above cocoa butter"s onset melting temperature (~30–34°C); heat transfer must occur primarily by conduction (not convection/radiation), and phase change must initiate at the interface and propagate upward due to thermal gradient.
(ii)Storyline: Frame 1: Intact chocolate block resting flat on pan surface, sharp edges, matte finish. → Contact initiates: no motion except passive thermal response. → Edge rounding begins at bottom corners, surface sheen appears. → Liquid film forms at pan-chocolate interface, visible as darkened/wet zone spreading laterally. → Solid portion gradually lowers and flattens while retaining cohesion; upper surface remains intact but thins. → All transitions occur continuously, monotonically, and exclusively from bottom-up; viewpoint remains fixed, frontal, and unobstructed; lighting stable and directional (top-down or front-lit).

Manual:
Experimental Procedure
1. Place a single rectangular chocolate block centered on a clean, dry, horizontal metal pan.
2. Gently apply mild heat to the pan base (e.g., low gas flame or hotplate) — no visible flame or glowing element required.
3. Record continuously for several minutes (e.g., 5–10 minutes) with a fixed frontal viewpoint, until the melt front has visibly risen through most of the block.
Observation of Experimental Phenomena
Chocolate surface softens: sharp edges round, corners slump, surface develops uniform wet sheen; bottom-contact region liquefies first, forming a thin liquid layer that spreads beneath the still-intact solid portion; no bubbling, charring, or separation.
Summary of Experimental Principles
Chocolate is a temperature-sensitive fat-based matrix; mild heating melts cocoa butter crystals (melting point ~34°C), causing solid-to-liquid phase transition starting at pan interface and progressing upward via conduction.

Prompt Grounding rubric:
level_1: No chocolate block appears; no metal pan appears; no heating action is shown; the chocolate is never placed onto anything; the scene has nothing to do with a chocolate block resting on a heated pan.
level_2: Only one of the required elements shows up (a chocolate block alone, or a bare metal pan alone, or a visible heat source such as a stovetop burner), but the chocolate is never placed onto the pan, and there is no sequence showing that contact beginning.
level_3: Both a chocolate block and a metal pan are present; the chocolate is placed onto the pan surface in one continuous motion; no hand, tool, or other object dominates the frame during that placement; the chocolate visibly rests on top of the pan afterward.
level_4: All of score 3, AND the chocolate stays fully within the pan's boundaries for the whole video; the pan itself never moves or tilts; the chocolate keeps the same position on the pan from start to finish (no sliding, tipping, or repositioning); the camera keeps a fixed, front-facing view that never becomes overhead or angled enough to hide the contact point.
level_5: All of score 4, AND the chocolate is centered on the pan; the pan surface reads as clean, uniform metal (shiny, non-porous); the chocolate keeps its original rectangular block shape at the start (no pre-existing melting or deformation); no logo, label, hand, or utensil ever enters the frame.

Scientific and Causal Correctness rubric:
level_1: The chocolate stays solid and looks unchanged throughout (no softening, no liquefaction): its color, shape, and surface texture are the same in the first and last frame.
level_2: The chocolate shows only a bit of surface gloss or slight edge rounding, with no real loss of structural integrity: no pooling, no flow, no sagging under its own weight, and nothing that reads as a solid-to-liquid transition.
level_3: The chocolate visibly softens: its edges lose their sharp lines, corners round off, and the surface picks up a wet sheen; it sags and deforms under its own weight while still holding together as one piece, with no pooling or flowing liquid yet.
level_4: All of score 3, AND small liquid patches appear where the chocolate meets the pan; the block continues to sag downward without breaking into pieces; the color stays the same brown throughout (no charring, browning, or scorching); there's no bubbling, steaming, or smoke.
level_5: All of score 4, AND the melted layer spreads upward from the pan-contact point, visibly wetting the pan and spreading outward beneath the remaining solid; the solid portion keeps shrinking in height while its top surface stays intact as one piece rather than breaking into separate liquid and solid islands; the whole sequence reads as one continuous, one-way progression: solid, then softened, then liquefied at the base, with the melt line climbing upward over time.

Spatiotemporal Consistency rubric:
level_1: The chocolate or the pan jumps to a different position or vanishes between shots; the room lighting suddenly changes character (e.g., daylight to night) with no cause; the pan's orientation flips mid-video; or there's a frozen/dropped frame long enough to break the sense of continuous time.
level_2: The chocolate shifts sideways with no motion blur or visible cause; the pan flickers in and out of view; the lighting's brightness or color shifts inconsistently between frames; the chocolate's surface jumps from matte to glossy with no heating progression shown to explain it.
level_3: The chocolate and pan stay fully visible and continuous the whole time, with the pan rigid and stationary; the lighting keeps the same direction and color tone throughout; any motion of the chocolate, such as gentle sagging, is smooth and physically plausible rather than floating, jerking, or teleporting.
level_4: All of score 3, AND the chocolate's deformation moves through its stages in order with nothing skipped (it never jumps straight from a sharp-edged solid to a pooled liquid); there's no tearing, warping, or geometric glitching between frames; the shadow the chocolate casts stays consistent with one fixed light source and the pan's unchanged position.
level_5: All of score 4, AND every later frame shows the chocolate at least as melted as the frame before it, with no re-solidifying, surface drying, or back-and-forth; the pan's reflections stay consistent with a fixed metal surface under constant lighting; the chocolate's surface finish changes in a believable order (matte, then a glossy sheen, then specular highlights) as the melted layer thickens.