My mechanic dog has neither tannable skin nor a brain, so I'm not sure if it has any effect on the game. However, I'd like to understand it. I'm pretty sure the game is trying to reference a tissue that doesn't exist, but I'm not sure what to do about it.
*** Error(s) finalizing the creature CLOTH_DOG
undefined local creature material set to default: CLOTH_DOG LEATHER
undefined local creature material set to default: CLOTH_DOG BRAIN
CLOTH_DOG:DEFAULT:right front leg, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left front leg, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right front paw, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left front paw, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right rear leg, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left rear leg, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right rear paw, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left rear paw, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:tail, layer 4: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right ear, layer 2: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left ear, layer 2: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:nose, layer 2: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:upper spine, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:middle spine, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:lower spine, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:skull, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left true rib, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right true rib, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left false rib, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right false rib, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:left floating rib, layer 1: Tissue was not found, using first tissue instead
CLOTH_DOG:DEFAULT:right floating rib, layer 1: Tissue was not found, using first tissue instead