pull back the sheets on his bed and dump a box of corn flakes in it, then make the bed back up.
and/or
take all his fish out and add food color to the tank. and/or
take his dogs to a kennel for the day he gets back and tell him that the dog catcher came to get them because it was reported that they bit someone and they had to be put down.
Yeah, I read too many of Lori's posts.