Domain: Engineering — Materials Science & Engineering
Target concept: Dry spaghetti fractures by bending (brittle fracture)

Video generation prompt: A person holds a dry spaghetti strand horizontally above a regular table with both hands, bending it inward in a smooth motion from the center.

Evaluation guide:
(i) Target concept: Brittle fracture under bending-induced tensile stress in a quasi-one-dimensional ceramic-like material, including the cascading multi-fracture (snap-back) effect characteristic of pure bending without twist.
Minimum mechanism: The material must be dry (low moisture → high Young's modulus, low strain-to-failure), geometrically slender (L/d >> 10), and isotropic; bending must generate monotonic tensile stress concentration exceeding ultimate tensile strength at the neutral-axis extremum near the center; because no twist is applied, the initial fracture releases a flexural stress wave that typically produces one or more secondary fractures in the resulting segments rather than a single clean split.
(ii)Storyline: [Frame 1–3] Strand held taut and horizontal, hands stationary at ends, full length visible above table. [Frame 4–6] Hands begin symmetric inward motion; strand develops visible central curvature while remaining intact. [Frame 7–8] Curvature increases continuously; no yielding or sagging. [Frame 9] Fracture initiates at or near the center. [Frame 10] Within the same instant, the released elastic energy triggers a rapid cascade of one or more additional fractures along the two initial segments, typically leaving three or more fragments rather than a single clean break; fragments may show brief secondary motion (small rotation or separation) immediately after fracture. [Visibility constraint] Entire strand, both hands, and tabletop must remain fully visible and unoccluded in fixed frontal/slightly elevated viewpoint throughout; no close-up cuts or angle shifts.

Manual:
Experimental Procedure
1. Place a single dry spaghetti strand horizontally in air above a regular table.
2. A person holds both ends of the strand with one hand near each end.
3. Smoothly bend the strand inward from the center by moving both hands toward each other while keeping the strand level, without introducing any twist.
Observation of Experimental Phenomena
The strand does not simply snap into two clean pieces. It first fractures near the center; the sudden release of stored elastic energy sends a bending wave rippling outward through the two remaining segments, and this wave briefly overcurves the strand at one or more other points enough to break it there too. Within a fraction of a second, the strand typically ends up in three or more fragments rather than a single clean two-piece split.
Summary of Experimental Principles
Dry spaghetti is a brittle rod with little tolerance for stretching before it snaps. When the strand is bent from the center with no twist, the first fracture releases the elastic energy stored in the two halves as a whip-like flexural wave. That wave transiently curves the remaining segments beyond their own breaking point at one or more secondary locations, triggering additional fractures in a rapid cascade. This is why bending dry spaghetti without twisting it almost never produces a clean break into exactly two pieces.

Prompt Grounding rubric:
level_1: No dry spaghetti strand is visible; or no human hands appear; or no table is present in frame; or no bending action is depicted; the scene bears no resemblance to a person bending a strand of dry spaghetti (e.g., it shows cooking pasta, a liquid scene, or a strand being snapped vertically instead).
level_2: A spaghetti strand and a table are both visible, but hands are absent or are not holding the strand; or hands are present but not positioned near each end of the strand; or the strand is simply held/shown statically with no inward bending motion at all.
level_3: A single dry-looking spaghetti strand is held horizontally by two human hands, one near each end, with a table visible below; the hands begin moving toward each other (inward bending) while the strand stays roughly horizontal above the table.
level_4: All of score 3, AND the bending clearly originates from the strand's center (the hands converge symmetrically while the strand stays taut and roughly horizontal right up to the moment of fracture); no extraneous object blocks the view of the strand, hands, or table; the full strand length and both hands stay within frame throughout the bending action.
level_5: All of score 4, AND the strand looks visually intact (no visible pre-existing crack, kink, or permanent bend) right up until it fractures; the table, both hands, and the point where the strand breaks are all simultaneously visible at the moment of fracture, with no object or hand accidentally covering the break point.

Scientific and Causal Correctness rubric:
level_1: Spaghetti appears wet, cooked, rubbery, or otherwise inconsistent with a dry, brittle strand (e.g., glistening surface, permanent bend without breaking, translucent or swollen appearance); or no fracture occurs anywhere along the strand during the video.
level_2: The strand looks dry and brittle, but breaks without any inward bending (e.g., it snaps while stationary, during a lateral twist, or after being dropped); or the break occurs at an end near a hand rather than near the strand's center; or the fracture surfaces look smooth and rounded rather than sharp and jagged.
level_3: The dry strand fractures near its center into two or more pieces only after the inward bending motion has begun, while the hands are still moving toward each other; the fracture is abrupt, not a slow tear; the resulting fracture surfaces are sharp and jagged, consistent with brittle failure; no plastic bending or elastic rebound is visible beforehand.
level_4: All of score 3, AND the strand ends up broken into three or more separate fragments rather than a single clean two-piece split — i.e., in addition to the central break, at least one more fracture appears in one of the resulting segments as part of the same event, consistent with the released elastic energy triggering a secondary break; none of the fragments show a slow bend-then-tear.
level_5: All of score 4, AND the full cascade of fractures (the central break plus any secondary break) completes within essentially the same instant, as part of one continuous bending motion; all fragments keep straight, undeformed geometry except exactly at the jagged fracture surfaces; there is no fused or melted-looking break, no dust or crumbling suggesting crushing rather than fracture, and no fragment shows a smoothly curved, unbroken shape.

Spatiotemporal Consistency rubric:
level_1: The spaghetti strand vanishes and reappears between shots, or the hands or table blink in and out of frame; the strand's shape distorts unnaturally between frames (stretching, warping, or appearing to melt); the scene contains an obvious frame skip or jump partway through the bending action.
level_2: The strand or a hand appears to jump to a new position with no visible path of motion in between; the tabletop's angle or perspective shifts noticeably partway through the clip; a shadow cast by a hand or the strand points in a direction inconsistent with the rest of the scene; the strand is shown clearly bent in one moment and then fully broken in the next with no intermediate state of it being bent-but-still-intact.
level_3: The hands stay attached to the strand's ends throughout; the strand remains above the table and roughly horizontal until it fractures; the inward bending shows smooth, continuous convergence of the two hands with no sudden reversal, freeze, or restart; the fracture happens within the same unbroken motion sequence, not after a cut or pause.
level_4: All of score 3, AND the strand's outline stays continuous and unbroken right up until the fracture frame; neither hand loses visible contact with the strand before it breaks; the table's shadow and reflection stay consistent in appearance throughout; no hand or object briefly and inexplicably covers the fracture point and then uncovers it without any motion explaining the change.
level_5: All of score 4, AND the speed of the hands moving toward each other looks steady from start to fracture, without an unnatural slow-then-sudden-snap change of pace; the strand's curvature increases smoothly and continuously (no back-and-forth wobble) right up to the break; there is no camera pan, tilt, zoom, or viewpoint jump at any point in the clip.