Domain: Healthcare — Human Physiology
Target concept: The concentration of carbon dioxide in exhaled air gradually increases after breath holding.

Video generation prompt: Connect the carbon dioxide monitor to the subject's mouth and nose, and record the carbon dioxide concentration during normal breathing. Then, have the subject hold their breath for 10 seconds and exhale again, observing the change in carbon dioxide concentration.

Evaluation guide:
(i) Target concept: Breath-hold induces alveolar CO₂ accumulation, resulting in higher CO₂ concentration in the subsequent exhalation.
Minimum mechanism: Intact respiratory physiology (functional alveoli, diffusion-capable membranes, patent airways), functional CO₂ monitor capable of real-time sampling at airway opening, and temporal alignment between breath-hold duration and CO₂ equilibration time.
(ii)Storyline: Phase 1 (Normal breathing): Monitor attached, subject inhaling/exhaling rhythmically, display showing a stable baseline CO₂ reading (a number, or equivalently a bar/gauge level). Phase 2 (Breath hold): Subject seals airway, chest/abdomen motion stops, monitor display freezes or blanks, no change in the reading. Phase 3 (Exhalation): Lips part, chest descends, airflow begins, monitor display updates to a reading that is visibly higher than the baseline (a larger number, an added digit, or a higher bar/gauge level), and holds that reading for the duration of the exhalation. All phases occur from a fixed frontal/slightly angled viewpoint with continuous visibility of the monitor's display and the subject"s face/mouth/nose region; no cuts, edits, or viewpoint shifts permitted.

Manual:
Experimental Procedure
1. Connect CO₂ monitor to subject"s mouth and nose.
2. Record CO₂ concentration during normal breathing.
3. Subject holds breath for 10 seconds.
4. Subject exhales while monitor remains connected.
Observation of Experimental Phenomena
CO₂ monitor displays a lower reading during normal breathing, then a visibly higher reading (a larger number, an added digit, or a higher bar/gauge level) only after exhalation begins following breath hold.
Summary of Experimental Principles
The concentration of carbon dioxide in exhaled air gradually increases after breath holding due to CO₂ accumulation in alveoli during apnea.

Prompt Grounding rubric:
level_1: No CO₂ monitor is visible anywhere in the frame; the subject's mouth and nose are never shown covered or sampled by a monitor; no breath-holding action occurs; no post-hold exhalation is shown; none of the three required steps (baseline recording during normal breathing, a 10-second breath hold, and exhalation immediately after) appear in the video.
level_2: At least one of: a CO₂ monitor appears in the frame but is never brought into contact with or held at the subject's mouth/nose; the subject breathes normally with no monitor in view at all; a breath-holding pose appears without any preceding normal-breathing footage or without a following exhalation; or only one of the three required steps (baseline breathing, 10-second hold, post-hold exhalation) is shown, and even that one step is out of order.
level_3: All three steps appear in correct sequence: (1) a monitor is visibly held at the subject's mouth/nose during normal breathing, (2) breath hold (chest and abdomen stop moving, mouth/nose sealed), (3) exhalation with the monitor still in place, but one core object is wrong or missing, e.g., the device shown has no visible readout of any kind so it cannot function as a CO₂ monitor, or the monitor visibly comes off the subject's face during the breath hold and is shown reattached only once exhalation starts.
level_4: All three steps appear in correct sequence with correct objects: a CO₂ monitor with a visible readout (digital number display or analog bar/gauge) stays at the subject's mouth/nose, breath hold is shown as sustained stillness of the chest/abdomen with the airway sealed, and exhalation follows immediately with the monitor still attached, but one non-core setup flaw exists, e.g., the connecting tube or strap is briefly shown loose or kinked, the monitor sits slightly askew on the face without breaking its seal, or the subject's hair/hand partially covers the edge of the monitor for a moment.
level_5: All three steps appear in correct sequence with no deviations: the CO₂ monitor is clearly a purpose-built measurement device (visible tubing/mask and readout) held continuously and snugly at the subject's mouth/nose across all three phases; the subject shows unambiguous breath-hold (chest/abdomen still, lips closed, no airflow cues) that transitions directly into visible exhalation (chest descending, lips parting); the monitor's position relative to the subject's face never shifts, and the camera framing keeps both the monitor and the subject's mouth/nose/chest in view throughout with no cut or discontinuity.

Scientific and Causal Correctness rubric:
level_1: The monitor's reading never changes across normal breathing, the breath hold, and the post-hold exhalation (same number or bar level the whole time), or it shows a physically impossible reading (e.g., the display reads zero or goes blank while the subject is actively exhaling, or the reading drops instead of rising); no visual link between the breath hold and any rise in the CO₂ reading is shown at all.
level_2: The monitor's reading changes, but in the wrong direction (the reading after the post-hold exhalation is lower than or equal to the normal-breathing baseline) or at the wrong time (the reading rises while the subject is still holding their breath, before any exhalation begins, or it changes only during ordinary breathing with no change tied to the breath hold); the sequence shown visually contradicts the expected chain of breath hold leading to a higher exhaled CO₂ reading.
level_3: The monitor shows a visibly higher CO₂ reading after the breath hold than it did during normal breathing (whether shown as a larger number, an added digit, or a higher bar/gauge fill), and the rise is associated with the exhalation, but the reading first ticks upward while the subject is still visibly holding their breath (before any air is exhaled), or there is a long unexplained delay after exhalation starts before the reading moves, so the timing of the causal link is muddled even though its direction is correct.
level_4: The monitor holds a stable, visibly lower reading during normal breathing and holds a stable, visibly higher reading beginning only once exhalation starts after the breath hold, with no rise at all while breath is being held, but one non-core flaw remains, e.g., the display flickers between the two readings for a moment before settling on the higher one, or the size of the jump looks implausibly large for only a 10-second breath hold.
level_5: The monitor shows: (a) a steady, visibly lower CO₂ reading throughout normal breathing, (b) no change to that reading for the entire 10-second breath hold (a frozen or blanked display during this phase is acceptable), and (c) a steady, visibly higher CO₂ reading that appears only once exhalation begins and holds for the duration of the exhalation, with the increase clear enough at a glance (a larger number, an extra digit, or a distinctly higher bar/gauge fill) that a viewer can tell the CO₂ reading rose without needing to read exact digits; no flicker, reset, or reversal occurs at any point.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal breaks: the subject or the monitor abruptly jumps to a different position, or the shot cuts to a different camera framing mid-sequence, with no continuous transition; the subject's head rotates more than 90 degrees between one moment and the next with no motion shown in between; the chest/abdomen's motion reverses instantly (e.g., snaps from mid-exhale straight to a fully held chest with no gradual transition); the ambient lighting abruptly and drastically shifts brightness between one frame and the next with no visible cause (e.g., a sudden flash to darkness or the reverse); or playback stutters or freezes for more than 3 consecutive frames.
level_2: Moderate breaks: the monitor is shown detached from the subject's face and then reattached at a visibly different position with no continuous transition between the two; the subject's chest/abdomen shows no visible movement at all during the 'normal breathing' phase; the background or camera framing shifts or zooms with no narrative reason to do so; the subject's eyes are shown closed in one moment and fully open in the very next moment with no blinking motion shown connecting them, implying a hidden cut; or the shadow cast on the subject or scene shifts direction between phases with no change in light source to explain it.
level_3: Minor but detectable breaks: the subject's hand touches or adjusts the monitor during the breath-hold phase, breaking the required stillness; slight camera wobble appears during the exhalation phase; one moment shows the monitor's readout partly blocked by hair or a hand; the chest's breathing rhythm is inconsistent from one breath to the next during normal breathing, yet the monitor stays aligned with the subject's face and the overall camera viewpoint stays fixed.
level_4: All motion is physically plausible and temporally continuous: the chest/abdomen rises and falls smoothly during normal breathing, stays still throughout the breath hold, and shows a gradual descent together with the lips parting at the start of exhalation; the monitor stays aligned with the subject's face across all three phases with no repositioning; the camera framing stays stable throughout, but one minor inconsistency remains, e.g., a strand of hair moves in a direction that doesn't match the exhaled airflow, or the monitor's strap/tubing visibly shifts tension with no corresponding head movement to explain it.
level_5: Zero spatiotemporal flaws: the camera viewpoint never pans, tilts, cuts, or zooms across the whole clip; the ambient room lighting and the monitor's display glow stay visually constant in brightness from normal breathing through the breath hold and into exhalation; the subject's facial features, the monitor's position on the face, and the torso's orientation show no visible drift, resizing, or repositioning in any frame except for the physiologically expected motion (rhythmic breathing, then stillness, then exhalation); all motion is smooth, moves in a consistent direction, and matches natural human breathing mechanics; nothing is occluded, flickers, or visibly deforms.