Domain: Humanities and Social Sciences — Linguistics
Target concept: Demonstration of the difference between voiced and voiceless stops through the movement of a candle flame during speech

Video generation prompt: A speaker sits at a table with a burning candle placed a few centimeters in front of their mouth, alternately producing voiced and voiceless stop syllables toward the flame.

Evaluation guide:
(i) Target concept: Differential aerodynamic output of voiced vs. voiceless stop consonants due to presence/absence of vocal fold vibration during oral closure.
Minimum mechanism: Vocal folds must be adducted and vibrating for voiced stops (damping pressure), and abducted and silent for voiceless stops (enabling pressure accumulation); oral closure must be complete and released abruptly in both cases; airflow must be directed toward candle without obstruction.
(ii)Storyline: [Phase 1] Stable baseline: speaker seated, candle lit and steady, mouth closed; flame motionless. [Phase 2] First articulation: mouth closes → holds → releases with burst → flame displaces (magnitude depends on voicing). [Phase 3] Brief recovery: flame returns toward rest position while mouth resets. [Phase 4] Second articulation: mouth closes → holds → releases with contrasting burst → flame displaces with different magnitude. [Phase 5] Final stability: flame settles. All phases must occur in fixed frontal view, with candle continuously visible and unoccluded; no off-screen actions; causal chain must be visually traceable from mouth release → air pulse → flame displacement.

Manual:
Experimental Procedure
1. Speaker sits upright at table, facing forward.
2. A lit candle is placed on the table, centered and adjacent to speaker’s mouth (few cm in front).
3. Speaker alternately produces one voiced stop syllable (e.g., /ba/) and one voiceless stop syllable (e.g., /pa/), releasing each with clear oral closure and burst.
Observation of Experimental Phenomena
The candle flame deflects visibly during the voiceless stop release due to strong airflow, but shows little or no deflection during the voiced stop release due to concurrent vocal fold vibration suppressing oral pressure buildup.
Summary of Experimental Principles
Voiced stops (/b d g/) involve vocal fold vibration during closure, reducing intraoral pressure; voiceless stops (/p t k/) involve no vibration, allowing high-pressure buildup and explosive release — demonstrated by differential flame displacement.

Prompt Grounding rubric:
level_1: None of the required setup elements appear: no lit candle, no seated speaker, no table, and no mouth movement directed at a flame: nothing in the frame resembles the candle-and-speech setup at all.
level_2: A candle and a speaker are both visible, but the candle is not positioned a few centimeters in front of the speaker's mouth (e.g., it sits off to the side, far away, or on a surface other than the table), or the speaker's mouth never opens toward it, so no articulation is attempted near the flame.
level_3: The speaker is seated at a table with a lit candle placed a few centimeters directly in front of the mouth, and the mouth is seen opening and closing at least once, but only a single articulatory event occurs, or repeated mouth movements look identical with no distinct closure-then-release burst, so no voiced/voiceless contrast could be attempted or identified.
level_4: The full setup is correct (seated speaker, table, candle a few centimeters from the mouth with an unobstructed path to the flame), and two separate articulatory events occur in sequence, each with a visible mouth-closure-hold-release cycle, but the two events are not visually distinguishable as one voiced stop and one voiceless stop (e.g., both appear to be the same syllable type, or the contrast in lip/jaw action is not legible).
level_5: All conditions for score 4 are met, and the two articulatory events are visually distinguishable as different syllable classes: one shows a voiceless stop (e.g., /pa/, /ta/, or /ka/, with a sharper, more forceful release) and the other a voiced stop (e.g., /ba/, /da/, or /ga/, with a visibly softer release), occurring one after the other without overlap, while the candle stays upright and fully visible throughout.

Scientific and Causal Correctness rubric:
level_1: The candle flame shows no meaningful response to mouth release at all: it stays essentially still throughout, flickers or extinguishes with no relation to when the mouth opens, or moves in a way unrelated to the timing of any release, indicating no aerodynamic link between the speaker's articulation and the flame.
level_2: The flame does react to mouth activity, but the timing or discreteness is wrong: its displacement starts before the release burst or continues through the closed-mouth hold phase, or the flame moves only once across the whole clip, or its motion blurs continuously across both syllables instead of appearing as two separate pulses tied to two distinct release events.
level_3: The flame visibly deflects once at each of the two release events, each deflection begins right at the moment of release (not during the preceding closure) and the flame returns close to its resting position before the next release, but the two deflections look the same size, with no visible difference between the voiced-stop trial and the voiceless-stop trial.
level_4: The flame deflects at each release as in level 3, and the two deflections are now visibly different in size: one release bends the flame noticeably further from vertical than the other, but which of the two syllables (voiced or voiceless) produces the larger deflection is not shown consistently or correctly.
level_5: All conditions for score 4 are met, and the larger flame deflection is specifically tied to the voiceless stop (e.g., /pa/, /ta/, or /ka/) while the smaller deflection or near-stillness is tied to the voiced stop (e.g., /ba/, /da/, or /ga/), matching the expected pressure-buildup contrast, with no reversal of which syllable produces the bigger movement and no extra, unexplained flame motion.

Spatiotemporal Consistency rubric:
level_1: The candle or speaker vanishes or reappears partway through the clip, the speaker's seated position jumps between frames with no transition, the flame skips from one position to another with no motion visible in between, the room lighting swings abruptly from bright to dark (or dark to bright) between consecutive frames with no visible cause, or the table surface or mouth geometry visibly warps or distorts.
level_2: The candle or table shifts position or rotates for no reason tied to the speaker's actions, the flame's outline tears, stutters, or stretches unnaturally instead of flickering like a real flame, the speaker's head appears to move independently of the shoulders and torso, or the flame snaps back to its resting position instantly rather than settling back gradually.
level_3: The candle stays fixed in the same spot on the table relative to the speaker's mouth throughout the clip; the flame's sideways displacement and its return to rest both look smooth and continuous rather than jumpy; the mouth follows a natural closure-hold-release sequence for each syllable; and the candle and flame are never occluded or distorted by the speaker's hand, head, or the table edge.
level_4: All conditions for score 3 are met, and both articulatory events (the voiced-stop trial and the voiceless-stop trial) occur within one unbroken shot with no cut, camera move, or zoom; the speaker stays seated and facing the camera throughout, and the flame stays visible in every frame so the two events appear in correct time order with no skipped time.
level_5: All conditions for score 4 are met, and the flame's motion is physically consistent with a brief air puff opposed by the flame's own buoyant restoring tendency: it leans away quickly at the moment of release, then decelerates and eases back toward vertical rather than snapping back along a straight line, with no jitter, strobing, or unnatural speed changes in either the flame's or the speaker's motion.