When Merry and Pippin have finished eating from their separate bowls, each goes over to the other's bowl to check it out - just in case something has been missed, don't you know. They lick the second bowl quite intently.
Then they decide that hey, that other dog is sure paying a lot of attention to that other bowl - there must be a reason for that, and they go back to the original bowls. A few repetitions is usually enough, but sometimes this can go on for fifteen minutes.
I try to explain this to them, but they just don't listen.