Domain: Natural Science — Physics
Target concept: Place a marble in front of two plane mirrors joined at a right angle, and verify that three distinct images of the marble appear in the mirrors, with the number of images being fixed and unique.

Video generation prompt: Place two plane mirrors vertically and connect them at a right angle. Fix the mirrors to maintain an angle of 90 degrees. Use a small marble with a distinct asymmetric surface marking (for example, a colored swirl or a painted arrow) so its orientation is easy to identify at a glance. Position the marble near the angle bisector, in front of the mirrors, within the field of view of both mirror surfaces.

Evaluation guide:
(i) Target concept: Formation of exactly three virtual images via double-reflection geometry in orthogonal plane mirrors.
Minimum mechanism: Two rigid, contiguous, perfectly reflective planar surfaces meeting at a true 90° dihedral angle; a single small object bearing a distinct asymmetric surface marking (so mirror-flips and rotations of it are visually distinguishable), placed in the accessible region before the corner; observer viewpoint aligned to see both mirror interiors and the junction.
(ii)Storyline: [Phase 1: Setup] Two mirrors are brought together and locked into vertical, orthogonal alignment; junction line is straight and unbroken. [Phase 2: Placement] The marked marble is introduced and settled into position directly in front of the corner, centered laterally. [Phase 3: Stabilization] All elements remain motionless; lighting stabilizes. [Phase 4: Observation] Three discrete marble images emerge: left mirror image (marking mirror-flipped left-right), right mirror image (marking mirror-flipped left-right), and central junction image (marking rotated 180°); all simultaneously visible, coherently positioned, and persistent. Perspective is fixed frontal; no occlusion blocks any mirror surface or image region.

Manual:
Experimental Procedure
1. Place two identical rectangular plane mirrors vertically on a flat surface.
2. Join them firmly along one edge to form a rigid 90-degree corner.
3. Position a single marble bearing a distinct asymmetric marking (e.g., a spiral color swirl or a painted arrow) directly in front of the corner, centered along the angle bisector.
Observation of Experimental Phenomena
Three distinct, non-overlapping images of the marble appear: one in each mirror surface, and a third centered at the corner where the mirrors meet. The two single-mirror images show the marking mirror-flipped left-right relative to the real marble, while the central image shows the marking rotated 180°. All three images are simultaneously visible and stable.
Summary of Experimental Principles
When two plane mirrors intersect at 90°, incident light from an object undergoes up to two reflections (one per mirror), producing exactly three virtual images — two primary (single-reflection) and one secondary (double-reflection) — due to the fixed angular constraint and law of reflection. Because each reflection mirror-flips the image, the single-reflection images appear laterally reversed while the double-reflection image appears rotated 180° relative to the object.

Prompt Grounding rubric:
level_1: No two mirrors are shown, or there's no marble at all, or the mirrors don't meet at a corner, or the marble isn't placed out in front of where the mirrors meet.
level_2: Two rigid-looking reflective panels appear, but their shared edge is clearly not a right angle (too wide or too narrow), or the marble sits far off to one side or partly out of frame instead of near the corner.
level_3: The two mirrors meet along one clean straight edge, the marble sits somewhere in front of that junction, and the whole setup reads as vertical mirrors with a marble nearby; but exactly how close the marble is to the bisector, or whether its marking is visible, isn't clearly shown.
level_4: The two mirrors meet at a corner that clearly reads as a right angle, both stand upright and steady, the marble sits in front of the junction and roughly centered on it, its distinct marking is visible and unobstructed, and every element the prompt calls for (two mirrors, right-angle join, vertical stance, marble with its marking near the bisector) is unambiguously present.
level_5: Everything required for a 4 is present, plus: the marble sits close enough to equidistant from both mirror faces that the gap to each mirror edge looks the same in the frame, the junction line is crisp and unbroken with no gap or overlap, and nothing in the shot (occlusion, odd angle, or perspective skew) throws off that symmetry.

Scientific and Causal Correctness rubric:
level_1: No image of the marble shows up in either mirror, or only one image appears, or an image shows up somewhere physically impossible: for instance appearing to float behind the mirror's back surface rather than in front of it.
level_2: Exactly two images appear (one per mirror) with no third image at the corner; or three images do appear but one is a duplicate, sits off from where the geometry calls for, or the arrangement clearly doesn't match a 90-degree double-reflection layout.
level_3: Three separate marble images are visible (one in the left mirror, one in the right mirror, and one at the corner where they meet), each fully separate from the others with no overlap, and no extra or missing images.
level_4: The three images are visible and fully contained within their respective mirror areas; the marking on the left- and right-mirror images appears mirror-flipped left-to-right compared with the real marble, and the marking on the central corner image appears rotated 180° from the real marble; all three images look similarly sized and equally clear, consistent with simple reflection rather than any distortion.
level_5: Everything required for a 4 is present, plus: the left and right images sit symmetrically on either side of the bisector line, the central image sits right along that bisector, all three images stay visible for the entire clip with no flicker or dropout or drift in position, and none of the three images looks noticeably brighter or dimmer than the others.

Spatiotemporal Consistency rubric:
level_1: The marble or a mirror suddenly jumps to a new spot with no motion connecting the two positions; the mirror junction visibly breaks apart or bends partway through the clip; or the lighting swings sharply (e.g., a sudden flash or the whole scene going dark) with nothing in the scene to explain it.
level_2: The marble's placement motion looks jerky rather than smooth; a mirror edge blinks in and out of view for a frame or two; the junction line wobbles or briefly vanishes; or a highlight/shadow on a mirror surface jumps to a different spot with no change in light source or camera.
level_3: The marble stays put once placed, both mirrors stay rigid and fixed in position, the junction line stays continuous and unbroken, and the lighting on the mirrors and marble doesn't shift or flicker; nothing in the scene clips through anything else or warps out of shape.
level_4: Everything required for a 3 is present, plus: the marble's initial placement motion (if shown) moves in one smooth, continuous direction with no back-and-forth, the mirrors keep the same reflective look throughout with no sudden shift to a dull or see-through appearance, and the three reflected images shift in a way that stays consistent with the camera's fixed viewpoint.
level_5: Everything required for a 4 is present, plus: there's no visible shake, flicker, or shimmer along any mirror edge or the marble's outline, the three reflected images stay in step with each other with none lagging behind or drifting out of alignment, and the camera itself never pans, tilts, zooms, or refocuses; the viewpoint is completely locked for the whole clip.