Cheating dog

Two dog owners were bragging about the intelligence of their pets.

"The brightest dog I ever had," said one, "was a Great Dane that could play cards. He was a genius at poker, but I had him put to sleep."

"You had him put to sleep, a bright dog like that? A dog like that would be worth a million dollars."

"I had to," he replied, "I caught him using marked cards!"