I killed a dog on normal and it's laying on the ground but running... it looks really wierd AND funny.
also, he looks happy, which is extremely creepy on a zombified looking god
I'm afraid not much can be done. Make sure you've patched your game up, as the new patches might help stop this from happening.
That happened to me once, but I didn't get to stare at it long because I was killed by one of his friends
Its not really a bug, because its the ragdoll. For some reason the ragdoll didn't go static asoon as you killed the poor little thing