Nobody. But I often hear the, "it's too big too have fit inside the dog," argument over forums. And most people that I have talked to on gg or imdb seem to think it's an error on the part of fincher/editors for not picking it up.
Personally I don't think the thing that leaves the dog, is the same thing scene shedding it's skin immediately thereafter in one of the cuts right before it scampers off.