Twice in the last week our DDog has left behind a small weird poo after he's jumped up from sleeping. It looks like crumbled up biscuits - but obvs smells like poo! He's a rescue border collie cross, about 6-8 years old and has been fully housetrained for poo since we got him 5 months ago. He acts quite embarrassed when it happens as if he knows something has happened he shouldn't have done. Any ideas what could be causing this??