My 5 yr old grandson is smearing poop at home, no other locations. He hides it in his room, spreads it in the family room, on his toys, books, furniture, parents' bedroom...nothing is off limits to him. His parents have tried several strategies over the last three weeks including timeout, rewarding small periods of good behavior that added up over three days time to get a big reward (movie night with mom &dad) that he promptly sabotaged as soon as they put him to bed(got up and smeared poop in his room). They have investigated common causes for this but nothing fits. He is a very smart child but he can't tell them why either. They make him clean it which he hates but it is not a deterrent. There is an 18 month old sister. This little boy gets plenty of positive loving attention but both parents are frustrated and need a way to stop this behavior. Any suggestions?