Domain: Humanities and Social Sciences — Linguistics
Target concept: Comparing the airflow of a candle flame to aspirated and unaspirated stops

Video generation prompt: A person holds a lit candle a few centimeters away from the mouth, alternately saying pie and spy toward the flame.

Evaluation guide:
(i) Target concept: Aspiration contrast between voiceless stops in English, operationally defined by presence/absence of audible and aerodynamically detectable airflow burst.
Minimum mechanism: Human vocal tract must produce /p/ with strong transglottal pressure release (pie) versus /p/ with concurrent /s/ constriction suppressing subglottal pressure buildup (spy); flame must be sensitive enough to respond to laminar airflow >~0.5 m/s, and positioned within laminar jet range (~3–6 cm) of lips.
(ii)Storyline: [Frame 0–2] Stable setup: lit candle held at fixed distance in front of still mouth; flame upright and steady. → [Frame 3–4] Onset of "pie": visible lip closure then rapid release with outward airflow burst → flame deflects away from mouth. → [Frame 5–6] Recovery: flame returns to upright position before next utterance. → [Frame 7–8] Onset of "spy": visible /s/ frication followed by /p/ closure-release *without* burst airflow → flame remains motionless. → [Frame 9] Sustained stability during /aɪ/ of both words. Visibility constraint: entire mouth–flame–candle triangle must remain in sharp focus and unoccluded; frontal or 3/4 view required to resolve lip gesture and flame deflection direction.

Manual:
Experimental Procedure
1. Person holds a lit candle steadily, positioning flame 2–5 cm directly in front of mouth.
2. Person articulates "pie" clearly, directing airflow toward flame.
3. Person immediately articulates "spy" clearly, directing airflow toward same flame.
4. Repeat articulation sequence once more if time allows (within 10 s).
Observation of Experimental Phenomena
The flame deflects visibly away from the mouth during "pie" (aspirated /pʰ/) but remains stable with no deflection during "spy" (unaspirated /p/ in /sp/ cluster).
Summary of Experimental Principles
Aspirated stops (/pʰ/, /tʰ/, /kʰ/) release a strong puff of air, causing measurable airflow; unaspirated stops in English onset clusters (e.g., /sp/, /st/, /sk/) suppress aspiration, producing negligible airflow — enabling visual contrast via candle flame displacement.

Prompt Grounding rubric:
level_1: No candle or flame appears; no person is shown; the mouth is never brought near a flame; neither "pie" nor "spy" is attempted; the scene shows something unrelated entirely.
level_2: A lit candle and a person are both shown, but the mouth is not held close to the flame; or only one of the two words ("pie" or "spy") is attempted at all; or the flame is missing from the shot; or there is no visible mouth movement suggesting either word is being said.
level_3: The candle stays lit and steady, the person's mouth is positioned near the flame, and both "pie" and "spy" are each said once with the mouth clearly moving for each; however, the two utterances are not clearly set apart in time (they run together without a distinguishable boundary), or the flame sits noticeably closer to or farther from the mouth in one attempt than in the other.
level_4: The candle is lit and held at a consistent distance from the mouth; "pie" and "spy" are said as two clearly separate, alternating attempts; the flame stays visible throughout; the mouth's position relative to the flame looks the same going into each word; both words show visibly distinct mouth movements (e.g., lips press together and release for "pie"; an /s/-shaping of the lips is followed by a /p/ closure for "spy").
level_5: All of 4, plus: "pie" and "spy" follow each other with no more than a natural breath's pause between them; the mouth sits at the same side, distance, and angle from the flame for both words; the flame stays fully in view and unblocked for the entire clip; no hand, object, or extra motion crosses in front of the mouth-flame area at any point.

Scientific and Causal Correctness rubric:
level_1: The flame doesn't move for either word; or it moves by the same amount at the same time for both words; or the flame is extinguished for both; or no candle/flame is present at all; or the flame bends toward the mouth for either word (aerodynamically impossible for an outgoing breath).
level_2: The flame deflects away from the mouth during "spy" while staying steady during "pie": the reverse of the true contrast, since it is "pie" that carries the audible burst of air, not "spy", even though the direction itself is physically plausible; or a deflection of the same size and timing appears no matter which word is said; or the deflection lines up with the vowel rather than with the stop-release.
level_3: The flame deflects away from the mouth specifically during the stop-burst of "pie" and stays essentially steady during "spy" (the scientifically correct direction of the contrast), but the effect is only weakly or inconsistently visible (e.g., the mouth-flame view is partly blocked, the deflection is very small, or it doesn't repeat cleanly across the two utterances).
level_4: The flame clearly deflects away from the mouth during the aspirated release of "pie" and shows no deflection during the unaspirated release of "spy"; the deflection is a clear present/absent contrast rather than just a difference in size; it is confined to each word's consonant burst rather than spreading into the vowel.
level_5: All of 4, plus: the deflection during "pie" runs unbroken from the burst through to the flame's return to upright; the flame stays visibly motionless through the whole "spy" articulation, including both the /s/ portion and the /p/ closure-release; no stray flicker during "spy" could be mistaken for a burst of air; the flame only ever moves during the stop-bursts, never during either word's vowel.

Spatiotemporal Consistency rubric:
level_1: The candle or its flame vanishes and reappears between frames; the person's head or the candle jumps to a new spot with no transition shown; the flame's size or color changes suddenly with no visible cause; a shadow cast by the candle or hand disappears and then comes back partway through.
level_2: The candle drifts sideways or tilts inconsistently between the "pie" and "spy" attempts; the flame flickers with an unnatural, strobe-like rhythm; the mouth shifts up/down or side to side between the two words even though the head should be holding still; a hand or the frame edge blocks the candle for more than a moment and it isn't clearly the same flame once it reappears.
level_3: The candle stays at a steady height and tilt; the flame is visible in every frame; the person's head and the candle's position relative to the mouth stay put between "pie" and "spy"; the flame shows only the small, irregular flicker any real candle has, not a repeating scripted pattern; nothing about the candle, hand, or person cuts to a new position or vanishes mid-clip.
level_4: All of 3, plus: the candle's height, tilt, and distance from the mouth stay the same across both words, not just roughly similar; the flame's base and tip change shape only the way a real flame would (gentle sway, faint heat shimmer), never abruptly reshaping; the mouth-to-flame distance and angle look the same before, during, and after each word; the area around the flame and mouth shows no visible tearing, doubling, or warping.
level_5: All of 4, plus: the flame's outline and the mouth's outline move only as smoothly as real fire and real lips would: no visible jump, warp, or freeze-then-skip at any point; the candle, flame, and mouth keep the same depth and perspective relationship to each other across the whole clip, as if neither camera nor objects suddenly shifted; any shadow the candle or hand casts on the person's face or chin stays in the same place and direction throughout, never disappearing or relocating between the two words.