I assume that you are looking for some polite, effective way to prove them wrong. But why bother? A bland, non-committal response is more discouraging to people who seek to shock or delight their listeners with quirky pronouncements. Just say, “That’s nice,” and change the subject. If you feel you must state your own opinion of animal abilities, you could widen your eyes and say innocently, “Oh, my! Maybe you should speak with your dog’s vet about that” – and then change the subject.