This failure often appears where the tail base sits close to a thigh or pelvis in the rest pose. The tail looks acceptable until it swings, then a patch of hip, belly, or upper leg follows it. Smoothing the rump can hide the crease while spreading the unwanted tail influence farther.

Keep two test poses: the tail rotation that exposes the drag and a hind-leg bend that was already working. A useful repair must improve the first without damaging the second.

Prove which group moves the hip

  1. Pose the tail without the leg

    At a clean frame, rotate only the first one or two deform bones in the tail chain. If the same rump patch moves while the hind leg stays neutral, you have isolated a tail influence rather than a general hip-volume problem.

  2. Select one dragged hip vertex

    Enable vertex selection in Weight Paint Mode, or switch the mesh to Edit Mode. Open the 3D Viewport Sidebar's Vertex Weights panel and read every group on that exact vertex. Look for a tail-base group alongside the intended pelvis, spine, or thigh groups.

  3. Compare a nearby vertex that stays still

    Read a neighboring rump vertex outside the dragged patch. The difference between the two weight lists is stronger evidence than the heatmap color alone.

Do not rebind a mostly good creature

Automatic Weights computes influences from bone proximity. Running it again can replace good paw, wing, face, or belly weights while leaving the tail-to-hip overlap just as ambiguous.

Remove only the stray tail influence

Use face or vertex selection masking to select the dragged rump patch. Activate the confirmed tail vertex group, then subtract its weight or remove the selected vertices from that group. Feather the boundary only if the patch crosses the real tail-root transition; vertices on the tail itself still need a controlled tail-to-pelvis blend.

After the removal, run Weights → Normalize All on the selected region with the groups that already deform correctly locked. Blender's weight tools respect vertex and face selection masks, so the operation does not need to touch the whole animal.

Separate wrong weight from missing volume

If the tail no longer drags the hip but the tail base still pinches, the remaining defect is a transition-quality problem. Inspect the pelvis and first tail groups across the tail-root loop, smooth that local gradient lightly, and compare Preserve Volume on the Armature modifier.

A large fold, overlapping skin flap, or tail pressed tightly against the body may also need better rest-pose spacing or topology. Do not keep deleting weights when the exact vertex list is already correct.

Retest both motion ranges

  1. Sweep the tail

    Test left, right, up, and down through the intended tail range. Confirm the rump patch stays with the body and the tail root does not form a new hard seam.

  2. Bend the hind leg

    Return to the original leg pose. The hip and thigh should keep their earlier volume; the local edit should not transfer ownership from the leg to the spine or pelvis.

  3. Inspect the boundary vertices

    Read one vertex inside and one outside the repaired patch. Their group totals and transition should remain deliberate, not merely look acceptable in one frame.

Know when this is not a weight repair

If the hip vertex has no tail weight but still follows the tail, inspect constraints, drivers, shape keys, Bone Envelopes, and other modifiers. Motion without a matching vertex-group influence is not proof that the weight data is wrong.

The free SkinSmart analyzer checks armature vertex-group relationships. It does not diagnose every constraint, driver, shape key, or Geometry Nodes setup, and it does not guarantee that an arbitrary production rig can be repaired.

Download the free analyzer

References