different sets of facial muscles--and therefore produce different-looking smiles. This divergence explains the difference between genuine smiles and fakey, say-cheese smiles in photographs. People have trouble faking other genuine expressions, too, like fear, surprise, or an interest in someone's pet stories. To overcome this limitation actors either drill with a mirror and practice conjuring up facial expressions a la Laurence Olivier, or, a la Constantin Stanislavsky, they inhabit the role and replicate the character's internal feelings so closely that the right expressions emerge naturally.) The limbic system, and the temporal lobes generally, are also closely tied up with sex. Scientists discovered this connection in a roundabout way. In the mid-1930s a rogue biologist named Heinrich Kluver started some