Cooper's body wasn't covered in fur, so Heiji could see how he could make that GRIEVOUS ERROR.

"That sounds sinister. Magic like that don't come without a price. Best not to get yourself mixed in with that kind of trouble in the first place -- invest in a diet and some hair dye instead." He never could understand what it was with humans and their need to absorb fields of magical power bigger than their own head.

Then again, he could see Sasuke making the same mistake.