My dad trained his dog, a little rat terrier, to respond to the word "heresy."
So when the Jehovah's witnesses would come, he'd take their literature, turn to the dog and say something like, "Is this true or is it heresy," and she would leap into the air, snatch the literature out of his hand, and then beat it back and forth against the floor like she was killing a rat, right at the feet of the wide-eyed JWs.
My dad would then tell the JWs it was probably best if they left as the dog would not tolerate heresy.