Domain: Healthcare — Basic Immunology
Target concept: Immune Organs - Observation of Thymus Structure

Video generation prompt: Harvest mouse thymus tissue, and prepare 5-μm paraffin sections. Perform HE staining, deparaffinize to water, stain with hematoxylin followed by counterstaining with eosin for several minutes. Dehydrate, clarify, and mount the sections, then observe under a light microscope.

Evaluation guide:
(i) Target concept: Visual verification of thymus identity and integrity via standardized HE-stained histology.
Minimum mechanism: Thymus must be biologically intact (not autolyzed/digested), paraffin embedding must preserve architecture, HE chemistry must yield differential nuclear/cytoplasmic binding, and light microscopy must resolve cellular organization.
(ii)Storyline: [Frame 0–2] Dissection scene: mouse thorax opened, bilateral thymus lobes lifted intact with forceps. [Frame 3–4] Processing: thymus placed on cold plate, embedded in paraffin block, sectioned into thin ribbon. [Frame 5–6] Staining: slide immersed in hematoxylin (nuclei acquire blue hue), then eosin (cytoplasm acquires pink hue). [Frame 7–8] Mounting: coverslip applied, resin hardened. [Frame 9–10] Observation: microscope field centers on thymic cortex (dense blue nuclei) transitioning to medulla (pink epithelium + Hassall corpuscles); viewpoint remains fixed on slide, no camera movement, full focus on tissue architecture.

Manual:
Experimental Procedure
1. Harvest intact mouse thymus (pale pink, bilobed) from chest cavity.
2. Embed in paraffin, section at 5 μm, mount on glass slide.
3. Deparaffinize, hydrate, stain with hematoxylin (nuclei turn blue), counterstain with eosin (cytoplasm turns pink).
4. Dehydrate, clear, mount with resin.
5. Observe under light microscope: cortex (dense blue nuclei), medulla (paler, with Hassall corpuscles).
Observation of Experimental Phenomena
Microscopic view shows sharp cortical-medullary boundary; blue-stained lymphocyte nuclei in cortex; pink-stained cytoplasm in medullary epithelial cells; eosinophilic Hassall corpuscles present.
Summary of Experimental Principles
Thymus is a primary lymphoid organ; HE staining differentially labels nuclear DNA (blue) and cytoplasmic proteins (pink); histological architecture confirms immune function and maturation site for T-cells.

Prompt Grounding rubric:
level_1: No thymus tissue is shown, no paraffin section appears, no HE staining reagents (hematoxylin or eosin) are used, and no microscope view appears; the clip shows unrelated objects or actions instead.
level_2: At least one correct object appears (e.g., the mouse's opened chest cavity, a paraffin block, or a glass slide), but none of the core actions (harvesting, sectioning, staining, mounting, or observing) actually take place; there is no recognizable sequence following the steps in the prompt.
level_3: All five key objects appear: the mouse thymus (a pale pink, bilobed organ), a paraffin block, a microtome, a glass slide, and a microscope; at least three of the core actions are shown (removing the thymus from the mouse, sectioning it onto a slide, and viewing the HE-stained slide under the microscope), but one or more steps are out of order or missing a key visual cue, such as no visible blue-stained nuclei or pink-stained cytoplasm under the microscope.
level_4: All five key objects are present and visually distinct from one another; all four major steps appear in the right order: the thymus is detached from the chest cavity, cut into a thin 5-μm ribbon that is transferred to a slide, stained so that blue nuclei and pink cytoplasm are clearly visible under the microscope, and the mounted slide is shown under the light microscope, but there is one non-core flaw, such as an unclear deparaffinization step, a slightly soft-focus microscope image, or lighting that shifts a bit between shots.
level_5: All five key objects are present and instantly identifiable by their shape, color, and context; every step appears in the exact order given in the prompt with full visual clarity: the thymus is lifted out intact and placed in a dish, the paraffin section on the slide looks thin and even, the HE stain shows a crisp blue-versus-pink contrast under the microscope, and the final shot is a steady, centered, high-contrast microscope view of the thymic cortex and medulla, with no step skipped, no jump in time, no object swapped out, and no break in spatial logic.

Scientific and Causal Correctness rubric:
level_1: The microscope view shows tissue that clearly isn't thymus (e.g., liver, muscle, or an empty slide); the nuclei are not blue and the cytoplasm is not pink; nothing about the cell pattern resembles thymus: no cortex-versus-medulla contrast, no Hassall corpuscles, no dense-to-sparse lymphocyte gradient.
level_2: The microscope view contains cells but none of the thymus-specific architecture; the nuclei are stained some other color (purple, gray, or left unstained) instead of blue, and the cytoplasm is some color other than pink (yellow, brown, or colorless); there's no recognizable lymphoid tissue pattern and no sign that hematoxylin and eosin stained different structures differently.
level_3: The microscope view shows lymphoid tissue with blue-stained nuclei and pink-stained cytoplasm, confirming that HE staining took place, and the cell density looks consistent with thymus (packed with small lymphocytes); however, there's no visible spatial organization: cortex and medulla can't be told apart, there's no epithelial network, and no Hassall corpuscles are visible, so the staining is present but doesn't yet confirm thymic structure.
level_4: Everything at the 3-point level holds, and in addition: the view shows correct thymic layout, with a densely packed cortex of small lymphocytes with dark blue nuclei and little pink cytoplasm, and a paler medulla with epithelial cells and at least one Hassall corpuscle (a pink, rounded structure); the blue-versus-pink contrast is consistent within each cell type, but there is one minor architectural flaw, such as the medulla looking oversized relative to the cortex, or the Hassall corpuscle lacking a clean, uniform pink color.
level_5: Everything at the 4-point level holds, and in addition: the view shows a sharp, textbook boundary between cortex and medulla; the cortex is packed with small, round lymphocytes with intensely blue nuclei and almost no visible cytoplasm; the medulla has larger epithelial cells with paler nuclei and generous pink cytoplasm, plus at least one clearly defined Hassall corpuscle showing a central pink core with concentric layering; every color matches what HE staining should produce (hematoxylin marking DNA blue, eosin marking protein pink), with no color bleeding between regions, no reversal of the staining pattern, and no distortion of the tissue.

Spatiotemporal Consistency rubric:
level_1: A severe break: e.g., the thymus is already sitting on a glass slide before any dissection is shown; the microscope view appears before the slide has been stained; the slide jumps straight from the bench onto the microscope stage with no hand shown carrying it there; the image's brightness or color swings drastically between consecutive frames with no matching change in the scene's lighting; the two thymus lobes split apart mid-clip with no visible cutting action causing it.
level_2: Several medium-level breaks appear together, e.g., the thymus shrinks or changes shape for no reason before it is fixed in paraffin; a stain color appears on the tissue with no liquid ever shown being applied; the microscope's field of view flips from upside-down to right-side-up (or the reverse) with no camera rotation shown; the action freezes for several frames during an active step like cutting or staining; the slide disappears between the sectioning and staining steps and then reappears; or the slide visibly slides sideways on the stage with no hand or forceps shown moving it.
level_3: One minor flaw only: e.g., a brief, sub-second flicker during the microscope's focus adjustment that does not make the tissue hard to identify; or a slight, momentary blur as the slide is set down on the stage that doesn't interrupt its visible path; or a faint shift in shadow during the staining step that doesn't hide the slide or the tissue on it; apart from that single flaw, every object keeps a consistent size, orientation, and position throughout.
level_4: Everything at the 3-point level holds, and in addition: the thymus, dissection tools, paraffin block, microtome, and slide all stay in sensible, unchanging positions relative to one another throughout the procedure; every motion (cutting, staining, mounting) is continuous and looks physically plausible, with no floating objects or sudden changes in speed; lighting and shadows change only gradually and only in step with an actual action, such as a stain droplet landing or the microscope refocusing; there are no jumps between frames anywhere in the clip.
level_5: Everything at the 4-point level holds, and in addition: every object (the thymus, the slide, the tools) keeps a consistent identity, size, and sense of solid form in every frame; every motion, from lifting the thymus to lowering the coverslip, follows a natural hand-driven path; lighting changes track logically with the light source and camera the whole time, with no unexplained flashes or drops in brightness; the microscope's focus shifts only during the observation step and behaves like real focusing (blurring and then sharpening), and nothing in the frame jitters, stretches, or warps at any point.