As we crossed a bridge in Bushy Park that spanned a river, we saw a dog that was intently trying to recover its ball. The ball had gone into the river, and the dog wanted it back. It wasn’t planning on swimming for it though. Instead, it was trying to reach it from the bank. It wasn’t having any success, but this did not seem to be stopping it from trying. I have no idea how patient a dog can be and what its limits of frustration might be, but it didn’t have any success while we were there.