Domain: Natural Science — Physics
Target concept: When water is poured into the cup, the coin at the bottom becomes visible.

Video generation prompt: A opaque cup with a coin at the bottom is placed on a table; the camera is fixed at the same height as the table. Keep the camera stationary and slowly pour water into the cup.

Evaluation guide:
(i) Target concept: Refractive visibility of submerged objects due to light path bending at liquid-air interface.
Minimum mechanism: Transparent liquid must fill the cup to create a continuous optical path from coin to viewer; cup walls must remain opaque and non-transmissive; viewing angle must be fixed and shallow enough that direct line-of-sight to coin is blocked by cup wall in air, but enabled by refracted rays in water.
(ii)Storyline: [Phase 1] Empty cup on table, coin at bottom: coin fully occluded by cup wall from fixed frontal viewpoint. [Phase 2] Water begins entering cup: coin remains occluded until water reaches bottom. [Phase 3] Water covers coin: coin becomes continuously visible and remains so as water level rises. [Phase 4] Pouring stops: coin stays visible, water surface stabilizes, no disappearance or flicker. All phases observed from fixed, tabletop-level camera with no perspective shift or lighting intervention.

Manual:
Experimental Procedure
1. Place an opaque cup upright on a tabletop.
2. Position a coin flat at the bottom center of the cup.
3. Fix camera at eye level with the tabletop, facing the cup frontally.
4. Slowly pour clear water into the cup from above until water covers the coin.
Observation of Experimental Phenomena
The coin is not visible when the cup is empty; it becomes clearly visible once water fills the cup to cover the bottom.
Summary of Experimental Principles
Light rays from the coin refract at the water-air interface, bending toward the normal, allowing previously blocked rays to reach the viewer’s eye — making the submerged coin visible despite the cup wall being opaque.

Prompt Grounding rubric:
level_1: No opaque cup appears; no coin is visible at any point; there is no pouring of water; the camera is not held at roughly tabletop height; or the scene does not show a cup sitting on a table at all.
level_2: An opaque cup appears on some surface, but the coin is missing or is not sitting at the bottom of it; water is missing, or it enters the shot with no visible pouring source; or the camera's height shifts up, down, or sideways over the course of the video.
level_3: An opaque cup sits on a tabletop with a coin at its bottom before any water is added; water is visibly poured into the cup from above; the camera stays at roughly tabletop height the whole time; and the coin's presence is continuous from the start of the video: it is never shown appearing in the shot without ever having been placed there.
level_4: Everything needed for level 3 is present, plus: the coin stays completely hidden from view before water reaches it; pouring begins while the coin is still hidden; and the coin becomes visible only once water has actually reached it, never before.
level_5: Everything needed for level 4 is present, plus: the cup never shifts from its spot on the table; the coin stays centered at the bottom and entirely within the cup's footprint both before and after water is added; the water is poured in one continuous, unbroken stream from a single visible source (a pitcher or hand-held vessel); and nothing besides the pouring stream ever enters or leaves the frame.

Scientific and Causal Correctness rubric:
level_1: The coin is visible before any water is added, or it disappears once water goes in; the water itself makes the coin vanish, change color, or float; or the coin's visibility changes with no timing relationship to the water at all.
level_2: The coin starts out visible or half-visible before water is poured, then disappears once water is added; the water looks opaque or tinted; the coin shifts position, size, or orientation for no physical reason; or there is no clear timing link between water entering the cup and any change in the coin's visibility.
level_3: The coin is completely hidden at the start; water is poured in; the coin becomes visible during or after the water covers it; the coin does not move from its spot at the bottom; the water itself looks clear rather than colored; and there is no contradictory behavior such as the coin floating, warping, or changing color.
level_4: Everything needed for level 3 is present, plus: the coin only becomes visible after water has visibly covered the bottom of the cup, never before; the water's surface is level and settled by the time the coin becomes visible; and the coin is not revealed by some unrelated visual quirk (a stray glare or lighting flare) rather than by the water itself.
level_5: Everything needed for level 4 is present, plus: the coin's transition from hidden to visible happens once, smoothly, with no flickering in and out; the water level rises steadily and evenly as it is poured; the coin stays sharply defined and correctly proportioned at every stage; and there is no optical artifact that real refraction could not produce: no doubled image, no color fringing, no unrealistic magnification of the coin.

Spatiotemporal Consistency rubric:
level_1: The cup suddenly jumps to a different spot or spins in place between frames; the coin abruptly appears in a different position or shape with no motion carrying it there; water appears or disappears with no visible source or stream connecting the two states; the room's brightness or shadows behave as if a different light source suddenly took over; or the tabletop surface itself buckles or breaks apart.
level_2: The cup wobbles or slides without anything pushing it; the coin's position relative to the cup's bottom shifts during pouring; the water stream cuts out or flickers between frames; the shadow cast by the cup or coin swings to a different angle or vanishes inconsistently; or background objects warp or distort.
level_3: The cup stays put on the table; the coin stays fixed at the bottom of the cup; the water pours as one continuous, unbroken stream; the cup and tabletop reflect light the same way from the first frame to the last, with no sudden brightening, dimming, or new light source appearing; and the shadow the cup casts on the table keeps roughly the same size, shape, and position throughout.
level_4: Everything needed for level 3 is present, plus: the water settles into a stable, flat surface once poured; there is no visible shaking or trembling in the cup's or coin's position from one frame to the next; the coin's apparent depth stays consistent with the cup's rim, with no mismatched parallax; and the water level does not start rising before the stream actually touches the cup.
level_5: Everything needed for level 4 is present, plus: the pouring motion looks perceptually smooth throughout, with no strobing or skipped frames in the stream; the cup's rim keeps a consistent round or elliptical shape from whatever angle it is shown; splashes and ripples behave like real water settling, never freezing unnaturally mid-motion; and every spatial relationship among cup, coin, water, and table stays intact for the full duration.