Dear Dr. Boli: Why can you point out something to a dog with your foot, but not your hand? —Signed, Mixed Signals in Morningside.
Dear Sir or Madam: It is because your dog has become accustomed to the idea that your hand may conceal something you intend to eat—something that, at any moment, the gravity gods may liberate from your hand and drop as a blessing from heaven upon the dog. Therefore, if you attract the dog’s attention to the hand, of course your dog’s attention will be fixed on the hand. Feet, on the other hand (so to speak), never do anything useful for dogs except walk you to the place where the food is kept, so your dog’s attention is free to notice the thing you point at with your toe. This fact of canine psychology tends to make the simple act of pointing out a crumb on the floor into a kind of ballet, which is very entertaining for the other members of your household—especially your cat if you have one.