Cross-eyed Dog

A man takes his Rottweiler to the vet.
He says, "My dog's cross-eyed, can you do something for him?"
"Let's have a look at him," says the vet, as he picks up the
dog, examines his eyes, and checks his teeth.
"I'm going to have to put him down," he finally says.
"What?" says the man, "just because he's cross-eyed?"
"No," replies the vet, "because he's really heavy!"