Domain: Natural Science — Morphology
Target concept: Animal skin color change through chromatophores (e.g., the response of chameleons)

Video generation prompt: Place a live chameleon on a branch located above a green leaf-covered surface, and then under stable lighting conditions, take continuous photographs from the same angle as it is moved to a brown wooden surface.

Evaluation guide:
(i) Target concept: Physiological skin-color change in a chameleon driven by structural iridophore mechanisms, observed here as a shift in hue that follows the color of the surface beneath the animal.
Minimum mechanism: The chameleon must be biologically intact (not painted, edited, or synthetic) and capable of the same general structural-color mechanism chameleons use for color change, actively adjusting the spacing of light-reflecting nanocrystals within a layer of skin cells (iridophores) — which in chameleons is used mainly for social signaling (e.g., contests, courtship display) and thermoregulation, and only secondarily contributes to background-influenced camouflage; the green leaf-covered surface and the brown wooden surface must be spectrally distinct and visually homogeneous so that this demonstration can isolate background hue as one stimulus capable of biasing the resulting skin color; no external manipulation (dye, lighting filters, or post-processing) may cause the color change.
(ii)Storyline: Frame 1-3: chameleon placed on the branch above the green leaf-covered surface -> its skin gradually shifts toward a green-dominant hue. Frame 4-6: chameleon repositioned along the branch (with visible motion) -> its skin hue fades toward a neutral baseline during the transit. Frame 7-10: chameleon placed on the same branch above the brown wooden surface -> its skin gradually shifts toward a brown-dominant hue. Throughout: fixed viewpoint, steady lighting, no occlusion of the two key surfaces, the chameleon stays fully visible and angled enough to assess its skin color; the green and brown surfaces stay within the same visual field (adjacent or side by side) so an observer can compare the two color states directly.

Manual:
Experimental Procedure
1. Place a live chameleon on a branch positioned directly above a green leaf-covered surface.
2. Maintain a fixed camera angle and stable lighting.
3. Reposition the chameleon onto the same branch, now positioned directly above a brown wooden surface.
Observation of Experimental Phenomena
In this demonstration, the chameleon's skin tone shifts toward the hue of the surface beneath it: greener while above the green leaves, browner while above the brown wood.
Summary of Experimental Principles
Chameleons change color by actively adjusting the spacing of light-reflecting nanocrystals within a layer of iridophore cells in their skin, producing rapid structural-color shifts. This mechanism is used mainly for social signaling (e.g., contests, courtship display) and thermoregulation (darkening to absorb heat, lightening to reflect it), and only secondarily contributes to background-matching camouflage. The color shift shown here toward the surrounding surface's hue illustrates this background-influenced component of the broader iridophore-based system, not the chameleon's primary use of it.

Prompt Grounding rubric:
level_1: No chameleon appears; or no branch appears; or neither the green leaf-covered surface nor the brown wooden surface appears; or the video never shows the chameleon placed above the two different surfaces in sequence.
level_2: The chameleon and a branch appear, and one of the two surfaces (green leaf-covered or brown wooden) appears, but the other surface never appears anywhere in the clip; or the branch is not clearly identifiable as a branch; or the camera angle changes between the two placements instead of holding steady.
level_3: The chameleon, a branch, the green leaf-covered surface, and the brown wooden surface are all shown; the chameleon is shown on the branch above one surface and later shown on the branch above the other surface; however, the two surfaces are not shown within the same continuous scene (e.g., there is a hard cut between the two setups, the lighting changes between them, or the camera resets to a different position), so the two placements cannot be compared side by side.
level_4: All four elements are present (chameleon, branch, green surface, brown surface); the chameleon is shown on the branch above the green surface first and above the brown surface second, both within one continuous fixed-viewpoint shot with matching lighting; however, either the branch's position shifts noticeably between the two placements, or the chameleon's body orientation changes drastically (e.g., it turns to face a completely different direction), so the two views are not fully comparable.
level_5: All four elements are present and stable: the chameleon sits on the same branch in both placements, the branch itself never changes position in the frame, the green leaf-covered surface and the brown wooden surface are both visible within the same shot (e.g., positioned side by side, or shown one after the other without any camera cut), and the chameleon's move from above the green surface to above the brown surface happens without any camera zoom, pan, or angle change; nothing else enters or leaves the frame except the chameleon moving along the branch.

Scientific and Causal Correctness rubric:
level_1: The chameleon's skin color does not change at all between the two placements; or the color it takes on contradicts the surface it is above (e.g., it turns blue while on the brown surface, or purple while on the green surface); or the color shift happens before the chameleon is placed on a surface or after it is removed, rather than while it is on it; or the skin displays a non-biological pattern (e.g., stripes or polka dots) unrelated to the surface hue.
level_2: The chameleon's skin shows some color shift, but it runs opposite to the surface beneath it (e.g., the skin looks lighter on the green surface and darker on the brown surface with no green or brown cast); or the skin changes color only once and does not shift again when moved to the second surface; or the color change happens as an instant cut rather than a visible transition.
level_3: The chameleon's skin becomes visibly more green-toned while above the green leaf-covered surface, and visibly more brown-toned while above the brown wooden surface; however, at least one of these two states is off: e.g., the skin stays essentially unchanged on one of the two surfaces, or the color on one surface is too washed out or ambiguous (due to poor contrast or overexposure) to clearly tell apart from the chameleon's resting color.
level_4: The chameleon shows two clearly distinguishable skin-color states: on the green surface, a hue that is unambiguously green-tinted rather than yellowish or grey; on the brown surface, a hue that is unambiguously brown or tan rather than black or reddish; each state appears only after the corresponding placement and holds steady while the chameleon remains there, with no frame mixing green and brown patches in a way that looks arbitrary rather than a smooth transition; however, one of the two states is only mildly saturated, making it harder to distinguish confidently from the chameleon's neutral baseline color.
level_5: The chameleon shows exactly two fully distinct, strongly saturated skin-color states: a clearly green state while above the green surface with no brown undertone, and a clearly brown/tan state while above the brown surface with no green undertone; each state appears only after its corresponding placement, holds until the chameleon is moved again, and the shift between the two states is a smooth, gradual transition rather than an abrupt cut or a chaotic mix of colors.

Spatiotemporal Consistency rubric:
level_1: The chameleon jumps from one surface to the other with no visible path of motion between them; the branch is absent from the frame for part of the clip and then is back in place with no visible cause; the lighting flickers or its brightness/color noticeably changes partway through the clip; the green and brown surfaces appear under visibly different lighting conditions; or the chameleon's body visibly stretches, splits, or distorts between frames.
level_2: The chameleon appears to move without visible contact with the branch (e.g., sliding or floating); the branch visibly bends or wobbles in a way a rigid branch would not; the chameleon's shadow becomes detached or misaligned from its body; or the green surface and the brown surface differ noticeably in sharpness or perspective from one another (e.g., one looks flat and blurred while the other looks sharp and angled).
level_3: The chameleon moves along a continuous, visible path from above the green surface to above the brown surface; the branch stays rigid and does not move or bend; the lighting stays steady throughout; however, a flaw remains, such as the chameleon briefly appearing to hang unsupported off the branch, its shadow briefly misaligning with its body for several consecutive frames, or one of the two surfaces showing persistent minor texture warping.
level_4: The chameleon stays in continuous contact with the branch throughout its repositioning; the branch shows no bending, vibration, or distortion; the light's direction and brightness on the chameleon do not visibly shift from one moment to the next across the whole clip; both surfaces keep stable texture and geometry; at most one small, isolated flaw remains, such as a single frame where the chameleon's foot appears to pass through the branch, or one frame where its shadow's edge jumps slightly with no matching change in the chameleon's position.
level_5: The chameleon's entire path of motion stays visibly grounded on the branch at all times; the branch's position and orientation look the same in every frame; the direction, color, and strength of the lighting stay constant throughout; the shadows cast by the chameleon and the branch stay aligned with a single consistent light source in every frame; the green and brown surfaces keep the same depth, texture detail, and relative scale throughout; there is no visible jitter, warping, stretching, or inconsistency in how the chameleon occludes or is occluded by the branch.