Domain: Healthcare — Human Physiology
Target concept: Flexor Reflex

Video generation prompt: A subject is seated comfortably with one hand resting on the table. The skin of the finger is gently stimulated with a blunt needle. Demonstrate a clear stimulus, an immediate response, and subsequent return to the resting state.

Evaluation guide:
(i) Target concept: Cutaneous flexor reflex in human upper limb.
Minimum mechanism: Intact sensory innervation of fingertip (median or ulnar nerve), functional spinal cord segment (C6–T1), intact motor innervation to finger flexors (e.g., flexor digitorum profundus/superficialis), and absence of cortical inhibition (ensured by relaxed seated posture).
(ii)Storyline: [Frame 0–2] Stable shot: seated subject, table, resting hand with extended fingers visible. [Frame 3–4] Stimulus tool enters view and makes unambiguous contact with volar fingertip pad. [Frame 5–7] Immediate, isolated flexion at DIP/PIP joints, no wrist/forearm motion. [Frame 8–9] Smooth relaxation and full return to initial extended posture. Perspective: Fixed frontal/slightly oblique view showing hand, finger, and tool; fingertip must be fully visible (no occlusion by thumb, tool, or examiner"s hand); lighting enables clear contrast between skin, nail, and tool.

Manual:
Experimental Procedure
1. Subject sits upright, one hand flat on table, fingers extended and relaxed.
2. Examiner holds a blunt needle and gently touches its blunt tip to the fingertip pad (volar surface).
3. Observe immediate finger flexion, then full return to resting posture.
Observation of Experimental Phenomena
- Stimulus contact appears as brief, localized indentation or touch on fingertip skin.
- Finger flexes visibly at distal and/or proximal interphalangeal joints within same visual interval as contact.
- Flexion ceases and finger fully re-extends to original relaxed position.
Summary of Experimental Principles
The flexor reflex is a polysynaptic spinal reflex elicited by cutaneous stimulation; it produces rapid, involuntary flexion of the stimulated digit via dorsal root → spinal interneuron → ventral horn motor neuron → flexor muscle activation.

Prompt Grounding rubric:
level_1: No seated human subject is shown; or no table is present; or no hand rests on the table; or the finger is not visible; or no blunt needle (or similar blunt-tipped probe) is present; or no stimulation action is depicted at all.
level_2: A seated subject and a table are both visible, but the hand is not resting on the table, or the finger is not clearly visible, or the blunt needle is missing from the shot, or no stimulation action is shown.
level_3: The subject is seated with one hand resting flat on the table; the stimulated finger is clearly visible; a blunt needle (a slender, blunt-tipped probe, not a striking reflex hammer) is present and held near the finger; the tool makes contact with the finger's skin.
level_4: All of 3-score, plus: the tool is recognizable as a slender, blunt-tipped probe rather than a mallet-like striking instrument, and its non-sharp tip, not a point that would visibly puncture, is what touches the skin; the hand stays in the same resting position before and after the stimulus; the finger is fully uncovered (no glove, wrap, or bandage).
level_5: All of 4-score, plus: the probe appears only once in the shot and is held solely by the examiner (never by the subject); its tip is oriented to touch the volar pad of the fingertip specifically (not the nail, the back of the finger, or a knuckle); and no other tools, hands, or body parts enter the frame during the stimulation.

Scientific and Causal Correctness rubric:
level_1: No finger movement is seen at any point; or a response phase is shown but the finger never returns to rest; or the finger's movement happens before the needle makes contact (stimulus and response are out of order or unrelated).
level_2: Finger movement occurs but is not in sync with the stimulus (e.g., it starts well before contact, or only after a long, distinct pause following contact); or the movement is not a flexion (e.g., the finger extends, spreads sideways, or just twitches randomly); or the finger never returns to its starting position.
level_3: The finger begins moving in the same continuous moment as the needle's contact; the movement is a visible flexion (the fingertip curls toward the palm); and the finger returns to its original relaxed, extended posture once the movement stops.
level_4: All of 3-score, plus: only the stimulated finger flexes; the neighboring fingers stay still, with no accompanying curl or spreading; the finger's return to rest is complete, with no lingering curl or tremor left in the fingertip afterward.
level_5: All of 4-score, plus: the flexion is concentrated at the fingertip's own joints (DIP/PIP) with no gross movement at the wrist or forearm accompanying it, even if the base knuckle (MCP) shows some slight accompanying motion; the whole sequence (contact, flexion building up, peak curl, relaxation, full rest) plays out as one continuous, unambiguous motion without a cut or freeze in the middle.

Spatiotemporal Consistency rubric:
level_1: The subject, table, or hand vanishes and reappears in a different spot without any visible transition; the finger's position jumps discontinuously between moments; the lighting or shadows change abruptly with no clear cause; the needle blinks in and out of view; or the hand/finger anatomy breaks (e.g., a joint bends backward, fingers fuse together, or a segment goes missing).
level_2: The hand or table shifts position slightly without a visible motion path; the finger appears to rotate unnaturally between moments; the needle's position jumps without a visible approach; the lighting shifts inconsistently across the shot; or background objects behind the subject warp or resize oddly.
level_3: The hand stays on the table and the finger stays attached to the hand throughout; the needle travels along a plausible path toward the finger; there is no abrupt lighting or shadow change and no distortion of the hand's or finger's shape.
level_4: All of 3-score, plus: the needle's approach to the finger follows a smooth, direct path (a straight line or gentle arc, not a zigzag or loop); the hand stays fully visible and unblocked for the whole sequence; the finger's flexion follows a natural hinge-like bend at its joints rather than looking like it slides or floats independent of the joint.
level_5: All of 4-score, plus: the camera framing stays fixed with no pan, tilt, or zoom; the subject's torso, shoulder, and elbow stay still with no compensating sway; the finger's motion stays within a simple forward-curling path with no unintended twisting or sideways drift; and the motion throughout looks fluid, without stutter or ghosting that would make the movement hard to follow.