Domain: Healthcare — Pathophysiology
Target concept: Hepatocyte Morphology in Fatty Liver

Video generation prompt: A fresh-frozen (cryostat) liver tissue section showing steatosis is placed on the experimental table, and observed under a light microscope using HE staining combined with Oil Red O staining.

Evaluation guide:
(i) Target concept: Visual identification of hepatocyte steatosis via dual-histological staining (HE + Oil Red O) under light microscopy, performed on a fresh-frozen (cryostat) tissue section, since routine paraffin processing would dissolve the neutral lipid droplets before Oil Red O could bind them.
Minimum mechanism: Lipid droplets must be chemically neutral (triglyceride-rich), reside exclusively in hepatocyte cytoplasm, lack limiting membranes, and be selectively bound by Oil Red O dye, producing a red chromophore visible against eosinophilic cytoplasm and basophilic nuclei.
(ii)Storyline: [0–2s] Fresh-frozen liver tissue section placed flat on experimental table; [2–4s] Light microscope positioned directly above slide; [4–6s] Microscope eyepiece view (or inset) reveals hepatocyte layer; [6–8s] Dual-stain contrast emerges: pink cytoplasm + blue nuclei (HE) co-localized with bright red spherical droplets inside cytoplasm; [8–10s] Stable view holds (red droplets remain confined within hepatocyte boundaries, nuclei visibly peripheral, no extraneous staining), confirming steatosis morphology. Perspective: Fixed overhead or oblique tabletop view; microscope eyepiece inset (if used) must maintain strict spatial correspondence (same field, same orientation, no parallax). Visibility constraint: All diagnostic features (droplet sphericity, intracytoplasmic location, nuclear displacement) must be unambiguously resolvable without zoom or annotation.

Manual:
Experimental Procedure
1. Place a fresh-frozen (cryostat-cut) liver tissue section showing steatosis on an experimental table — a routine paraffin-processed section cannot be used here, since paraffin processing (dehydration and xylene clearing) dissolves neutral lipids and would leave nothing for Oil Red O to stain.
2. Position light microscope for observation.
3. Observe the same tissue region under HE staining (pink cytoplasm, blue nuclei) and Oil Red O staining (bright red intracytoplasmic lipid droplets), both applied to the frozen section so tissue architecture and lipid content are preserved together.
Observation of Experimental Phenomena
- Hepatocytes show enlarged size and cytoplasmic crowding by discrete, spherical, bright red droplets.
- Nuclei are small, round, basophilic, and displaced peripherally.
- Cytoplasm is eosinophilic (pink/magenta), sharply demarcated from red droplets.
Summary of Experimental Principles
- Steatosis = accumulation of neutral triglycerides in hepatocyte cytoplasm.
- Oil Red O selectively stains neutral lipids red — this requires an unfixed, frozen section, since standard paraffin processing removes both the dye's lipid target and the ability of the dye to bind; HE stains proteins (cytoplasm) pink and nucleic acids (nuclei) blue/purple and works on either frozen or paraffin sections.
- Morphologic hallmark: lipid vacuoles displace nucleus to cell periphery without membrane enclosure.

Prompt Grounding rubric:
level_1: No liver tissue section is visible anywhere in the shot; no light microscope is present; the slide shows no staining at all (no pink/blue HE tones, no red Oil Red O tones); no experimental table is shown holding a specimen; none of the three required setup pieces (steatotic liver section, light microscope, stained slide) appear.
level_2: Only one of the required setup pieces appears (for example a microscope with no slide loaded, or a tissue section that is never placed on the table), and the placement-then-observation setup described in the prompt (tissue on table, microscope over slide, staining visible) is skipped, reordered, or only partially shown; the slide, if visible, carries just one stain tone (only pink/blue or only red) rather than both.
level_3: A liver tissue section is shown lying flat on an experimental table; a light microscope is positioned over or beside it as though set up for observation; the visible tissue area carries two distinguishable stain tones at once, a pink/magenta background tone (HE) and red-tinted rounded inclusions (Oil Red O), on the same patch of tissue; the tissue section, the microscope, and the dual-toned slide are all present together in a spatially coherent tabletop arrangement.
level_4: Everything in score 3 holds AND the tissue section and the microscope's eyepiece view (or an inset showing the magnified field) depict the identical tissue region, not two different fields, with the wide tabletop shot and the magnified view agreeing on which patch of tissue is being examined; the specimen is shown as a single frozen (cryostat) tissue section rather than as two separate slides, a paraffin block, or an unrelated reagent such as an antibody/IHC kit; framing stays wide enough that table, tissue, and microscope are visible together, not just a cropped close-up.
level_5: Everything in score 4 holds AND the tabletop and eyepiece views stay in a fixed, stable arrangement from the moment the tissue is placed through the moment it is observed, with no sudden jump in the position, scale, or apparent magnification of the tissue or microscope; the tissue section stays continuously visible throughout: it never disappears from one shot and reappears in another; the eyepiece/inset view and the tabletop view of the same tissue patch match in orientation and scale, with no mismatched magnification or misaligned overlay between the two views.

Scientific and Causal Correctness rubric:
level_1: No steatosis phenomenon is depicted at all: no lipid droplets of any kind, no color differentiation between hepatocyte cytoplasm and lipid content, no sign of nuclear displacement or hepatocyte swelling; or the staining colors directly contradict the assay (e.g., Oil Red O renders blue/diffuse instead of red, or HE nuclei render pink instead of blue/purple).
level_2: Droplet-like shapes are present but none are actually red, or red color is present but appears as a diffuse haze rather than discrete rounded droplets inside hepatocytes, or hepatocyte cell boundaries are too indistinct to tell where cytoplasm ends, or nuclei stay centered rather than pushed to the cell periphery, or the HE component shows no pink cytoplasmic tone at all, breaking the causal chain from staining protocol to droplet color to hepatocyte shape to a steatosis diagnosis.
level_3: Discrete red, rounded droplets sit inside hepatocyte cell boundaries; the surrounding hepatocyte cytoplasm carries a pink/magenta HE tone; nuclei appear small, round, and blue/purple; at least some hepatocytes show their nucleus pushed toward the cell edge with cytoplasm crowded by the red droplets, together reading as steatosis morphology on the same patch of tissue.
level_4: Everything in score 3 holds AND the red droplets sit only inside hepatocyte cytoplasm: none inside nuclei, none in the sinusoidal spaces between cells; no non-hepatocyte cell (e.g., Kupffer cells lining the sinusoids, endothelial cells) carries red staining; affected hepatocytes look visibly larger than any non-steatotic hepatocytes shown for comparison, or their enlargement is evident from how tightly the droplets crowd the cytoplasm; peripheral nuclear displacement is consistent across more than one affected hepatocyte, not just a single cell; there is no stray red precipitate, no red bleeding across cell edges, and no unexplained pink/red haze in the background.
level_5: Everything in score 4 holds AND every visible red droplet stays fully inside a clearly outlined hepatocyte, each droplet reading as round or oval rather than jagged or fused with neighbors; no red signal touches or overlaps a nucleus; the pink/magenta cytoplasmic tone stays even and unbroken around each droplet; no red tone appears in connective tissue or vessel walls in the background; nuclei keep their blue/purple tone in every steatotic cell shown; the overall picture matches the textbook description of fatty-liver hepatocyte morphology: ballooned cells packed with discrete, non-membrane-bound, neutral-lipid droplets stained red by Oil Red O, ringed by eosinophilic (pink) cytoplasm.

Spatiotemporal Consistency rubric:
level_1: The liver tissue section or the microscope vanishes from view and then reappears later in the sequence; the staining colors on the same tissue patch flip (e.g., the pink cytoplasm suddenly reads blue, or the red droplets suddenly read a different hue) with no staining step shown to justify it; the tissue visibly warps like paper, appears to melt, or spins freely as if unattached to the table; the camera viewpoint on the tabletop scene jumps to a completely different angle with no transition; or the overall lighting on the tabletop or microscope view abruptly brightens, dims, or shifts color with no visible cause.
level_2: More than two abrupt cuts or position jumps occur for the tissue, table, or microscope; more than one object (tissue section, slide, or microscope) blinks in and out of frame; the tissue surface wrinkles, stretches, or buckles with no hand or tool touching it; the microscope's apparent focus/zoom level changes without any corresponding change in how sharp or blurred the tissue detail looks.
level_3: At most one brief, self-resolving glitch occurs (for example a single stutter in playback, or a hand/tool briefly blocking the tissue before moving away cleanly) while the tissue section stays flat and rigid, the microscope stays in one place, and the tissue, table, and microscope keep the same relative arrangement to each other for the rest of the sequence.
level_4: No stutters, jumps, or flickers occur anywhere in the sequence; the tissue section, table, and microscope keep the same size, orientation, and position relative to one another throughout; the tissue stays lying flat with no sagging or lifting off the table; the microscope stays aligned over the same spot; there is no floating, sliding, or unsupported rotation of the tissue section or microscope.
level_5: Everything in score 4 holds AND the tabletop view and the microscope eyepiece/inset view (when both are shown) agree on the tissue's tilt and scale at every moment, with no mismatch in perspective between the wide shot and the magnified view; any camera or stage movement (e.g., a slow push-in toward the slide, or a focus pull) proceeds at a smooth, steady pace without sudden speeding up or stopping; the red droplets and the pink/blue staining stay visually steady in color and position from frame to frame as the view moves, without strobing or flicker.