there's a dog here that routinely tries it on for something more tasty than his dried dog food... he's going through one of those periods at the moment. will walk away from his food in the morning, pick at it during the day. Sometimes he won't eat any of it all day for several days, other days he lives up to his name (Dusty the Irish Wolf Hound) and the same food is gone in seconds.
He's on a diet, and knows it and tries it on routinely to get something more tasty....
He hasn't worked out we know what he is up to!