CRITICALFailure Reference

Runway ML Limb & Anatomy Artifact — Pre-Generation Risk Reference

Technical Classification

Anatomical Topology & Coherence Failure

Anatomical Topology & Coherence Failure occurs when Runway's diffusion model produces skeletal structures with non-manifold mesh topology — physically impossible configurations that cannot exist in the real world. This includes supernumerary limbs (extra arms or legs), interpenetrating geometry (limbs passing through each other), discontinuous joint articulation, and finger-count hallucination. It most commonly occurs with human subjects in motion, especially during dance, sports, or close-up hand shots.

How to identify this failure

✕Extra arm or leg appearing mid-clip
✕Fingers fusing together or splitting into more than 5
✕Elbow or knee bending in the wrong direction
✕Limb geometry collapsing or stretching unnaturally
✕Arm passing through torso

Real generation examples

Prompt used

"Ballet dancer performing a grand jeté across a sunlit stage"

Failure observed @ 1.2s

Third arm appeared at 1.2s, leg geometry collapsed at 4.1s

Prompt used

"Close-up of hands playing piano, dramatic lighting"

Failure observed @ 0:03

6 fingers on right hand, knuckle geometry collapsed at 0:03

Documentation strength

If you need to escalate

VERY HIGH — Runway support treats limb artifacts as a recognised critical failure mode with strong support-escalation precedent.

AVA is a pre-purchase prevention tool, not a post-purchase recovery tool. Platforms generally do not guarantee credit refunds for output-quality failures; goodwill credits are at each platform's discretion. The strength rating reflects how well-formed your support ticket can be, not a promised outcome.

Prevention + documentation steps

01
Score your prompt before you generate
Run your prompt through AVA's pre-flight scoring against the Anatomical Topology & Coherence Failure pattern. Green light = generate. Yellow/red = rewrite using the suggested fix before you commit credits.
02
Capture Generation ID + timestamp if it failed anyway
Find the Generation ID in the URL or share link. Note the exact time when the Anatomical Topology & Coherence Failure first appears (e.g. "failure first visible at 1.2s"). Timestamped evidence is significantly stronger than a general complaint.
03
Use the correct technical term in your support ticket
Describe this failure as "Anatomical Topology & Coherence Failure". This term maps to a recognised internal workflow in the support system and routes the ticket to the right team.
04
Submit via the correct support channel
Runway has no direct email intake. Pro+ plan: open the in-app AI Assistant (help widget bottom-right of app.runwayml.com), describe the failure with the technical term, attach evidence. Free/Standard plan: human support isn't available — your channel is Discord #community-help with @On Call - Moderators.

Frequently asked questions

Will Runway support escalate credits for limb artifact failures?

Yes. Runway support classifies limb artifacts as a recognised critical failure mode. Requests with a Generation ID, technical failure description (use "Anatomical Topology & Coherence Failure"), and a timestamped failure point are routinely approved.

Why does Runway generate extra limbs?

The diffusion model's denoising process can produce non-manifold geometry when multiple articulated bodies are in motion, especially in complex lighting. This is a known limitation of video diffusion models at current resolutions.

Which Runway prompts are highest risk for limb artifacts?

Dance sequences, sports, hand close-ups, multiple subjects, and any prompt with rapid movement. AVA's L1 scanner flags these automatically before you spend credits.

Catch it before you generate

AVA scores this failure mode against your prompt in real time

Free Chrome extension. Analyzes your prompt as you type, flags failure-prone patterns specific to this model, and tells you what to rewrite — before you commit credits to a generation that will fail.

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