Domain: Natural Science — Geology & Geophysics
Target concept: Fingernail scratch on a gypsum crystal

Video generation prompt: A person drags a bare fingernail across the flat surface of a light-colored gypsum crystal.

Evaluation guide:
(i) Target concept: Mechanical scratch test as a field method to estimate relative mineral hardness using human fingernail as standardized reference tool.
Minimum mechanism: Fingernail must be bare (no polish/glove), dry, and applied with light pressure; gypsum must be intact, anhydrous, and light-colored to ensure visibility of the subtle scratch; scratch must result solely from abrasive displacement of surface crystals, not cleavage, fracture, or chemical reaction.
(ii)Storyline: Frame 1–2: Static shot of light-colored gypsum crystal with clearly flat, unbroken facet in view. Frame 3–4: Bare human fingernail enters frame and makes initial contact at one edge of the flat facet. Frame 5–8: Fingernail drags continuously in straight-line motion across the facet: contact remains unbroken, pressure constant, no lifting. Frame 9–10: Drag completes at opposite edge; scratch is fully visible as a continuous, matte, color-matched line; no transient artifacts (e.g., dust cloud, moisture, reflection) accompany the action. Perspective: Fixed frontal or slight oblique angle (≤30°), ensuring full visibility of contact zone and scratch path; no occlusion by hand, fingers, or equipment; lighting is diffuse and shadow-consistent.

Manual:
Experimental Procedure
1. Place a light-colored gypsum crystal (pale white, cream, or light tan) on a stable surface with a clean, flat facet facing upward.
2. With bare, dry, unpolished human fingernail, gently press the nail tip onto the center of the flat facet.
3. Drag the fingernail steadily in one direction across the flat facet for ~5 cm — maintaining constant light pressure and continuous contact.
Observation of Experimental Phenomena
A continuous, shallow, matte, linear scratch appears along the drag path — identical in color to the crystal, with no chipping, powder, or subsurface damage.
Summary of Experimental Principles
Gypsum has a Mohs hardness of 2; human fingernail has a Mohs hardness of ~2.5, enabling it to scratch gypsum cleanly without fracturing or pulverizing the crystal — demonstrating relative mineral hardness via direct mechanical abrasion.

Prompt Grounding rubric:
level_1: No light-colored gypsum crystal is visible; no bare human fingernail is visible; no dragging action across a flat crystal facet occurs; gypsum crystal, bare fingernail, and flat facet never appear together in any shot.
level_2: At least one required element appears (a pale gypsum crystal OR a bare fingernail) but they never appear together in the same shot; or the dragging tool is not a bare fingernail (e.g., a pen, stylus, gloved finger, or metal tool), or the surface dragged across is not the crystal's flat facet (e.g., wood, paper, or a curved/broken edge).
level_3: The light-colored gypsum crystal and a bare human fingernail both appear in the same shot; the fingernail contacts the crystal's flat facet at least once and a dragging motion occurs along it, but either the crystal is not clearly pale (e.g., looks gray, brown, or smoky blue), the facet is not visibly flat (e.g., heavily fractured, domed, or coarsely grainy), or contact breaks into several separate touches rather than one sustained drag.
level_4: A uniformly pale white, cream, or light-tan gypsum crystal and a bare fingernail (no polish, no glove) both appear; the fingernail keeps continuous contact with a visibly flat, unbroken region of the crystal while dragging in essentially one direction for at least 70% of the visible motion duration; no extra tools, extra hands, or occlusions block the view of where nail meets crystal.
level_5: The pale, matte gypsum crystal and bare fingernail (no polish, no glove, no artificial nail) appear together; the nail starts at one edge of a flat facet and drags in a single straight path to the far edge without lifting, veering, or sliding off the facet; the whole drag is shown in one fixed shot of the crystal and fingernail, with no camera cut, pan, or zoom.

Scientific and Causal Correctness rubric:
level_1: No scratch appears where the fingernail dragged, and instead the gypsum crystal cracks, shatters, crumbles, or changes color at the contact zone; or the surface shows deep gouging, powdering, or a wet sheen, none of which matches gypsum's very low (Mohs 2) hardness being simply abraded by a slightly harder fingernail.
level_2: The fingernail drags across the crystal but leaves no visible mark at all; or the mark that appears is physically implausible for this pair of materials (e.g., the crystal appears to melt, bubble, or throw off a visible dust cloud); or the contact produces chipping/flaking rather than a smooth abrasion line.
level_3: A linear scratch appears along the drag path, visible as a continuous, shallow, matte line, but it is either too deep (revealing an inner layer, casting a visible shadow, or leaving raised ridges), too faint to read as a scratch under normal lighting, or breaks into disconnected segments of uneven width along the path.
level_4: The scratch is a continuous, evenly narrow, non-reflective line that tracks the fingernail's exact path; there is no chipping, flaking, powder, or color change anywhere next to the scratch, and the mark stays confined to the surface with no cracking or spalling beneath it.
level_5: The scratch reads purely as a shallow surface abrasion: a subtle but unmistakable streak the same hue as the crystal's base color, with even width along its whole length; no smearing, skin residue, or secondary fracturing appears anywhere; the mark exists only along the exact path and duration of the fingernail's drag, consistent with gypsum (Mohs 2) being cleanly abraded, not fractured, by a slightly harder (~2.5) fingernail.

Spatiotemporal Consistency rubric:
level_1: The gypsum crystal or the fingernail jumps to a different position or angle between shots with no motion connecting them; the lighting abruptly switches character (e.g., bright daylight to dim warm light) partway through; the crystal's facet changes shape outright (flat becomes domed becomes flat again); or the fingernail vanishes and reappears without ever moving there.
level_2: The fingernail's drag repeatedly freezes and jumps rather than sliding smoothly; the crystal's surface look changes mid-shot (e.g., smooth, then grainy, then glossy) with no cause; the lighting flickers, or the fingernail's shadow becomes clearly detached from where the fingertip actually is; or the camera suddenly reframes or rotates without a smooth transition.
level_3: The drag is mostly smooth and the crystal's look stays consistent, but there is one clearly noticeable pause or hitch in the fingernail's motion, or the shadow cast by the fingernail is visibly misaligned from the fingertip for a moment, a small, spottable flaw rather than a fully clean, continuous drag.
level_4: The fingernail's drag is continuous at a steady, even pace with no visible freezing or sudden acceleration; the crystal's texture, lighting, and viewing angle stay consistent throughout; the fingernail's shadow tracks its position and the light source coherently across the whole shot; there is no warping or dropped-looking motion.
level_5: The fingernail's motion looks completely natural and fluid, with no stiff or robotic quality; the crystal sits perfectly still with no shimmer or vibration; the light stays uniform in direction and brightness with no shadow drift; the camera holds one fixed framing throughout with no pan, tilt, zoom, or blur/ghosting between shots.