Rottweiler

A man takes his Rottweiler to the vet and says "My dog's cross-eyed, is there anything you can do for him? "

"Well," says the vet, "let's have a look at him". So he picks the dog up and examines his eyes, then checks his teeth.

Finally, he says "I'm going to have to put him down."

"What? Because he's cross-eyed? "

"No, because he's really heavy"