My dog is cross-eyed

A man takes his Rottweiler to the vet and says,

"My dog is cross-eyed.Is there anything you can do for him?"

The vet says, "Well, let's have a look at him."

So the vet picks the dog up while examining his eyes.

Finally the vet says "I'm going to have to put him down."

"What? Just because he is cross-eyed?"

"No, because he is really, really heavy."