Next time the baby shoots you a dirty look, it might not be gas. Instead, the baby might be really disgusted by your behavior. Interpersonal interaction is a major survival feature of the human species and so it's not surprising that we come hard-wired with the mental power to track relationships. The big news is that we also start very early to track how others play out those rules, even when the interaction has nothing to do with us. Babies have far more social smarts than we give them credit for. For instance, research on babies has shown for years that they recognize and prefer a human face. Put a Picasso face arrangement — with eyes where the nose should be — in their line of vision and babies look away in disgust. But present them with a real face or a picture of a real face, and they are captivated. Also, as early as 3 weeks of age, a baby can tell the difference between an object and a person, and they prefer the person. Babies are also adept social butterflies, born with the rules of engagement etched on their brains. Pediatrician T. Barry Brazleton has shown that there is a certain set rhythm to the social interactions of mothers and babies. They engage (what we often call "play"), then the baby cuts out and has down time, and then they start up again. The baby is designed to participate in this inter-personal tango (and so are adults), and mothers quickly know that something is wrong if the baby doesn't connect with her. Experiments years ago by Jeffery Cohn and Edward Tronick of Children's Hospital in Boston also showed that babies have a natural distrust of even their most trusted caretakers when the social rules are not followed. Mothers were instructed to not respond when the baby reached to get her attention for a little one-on-one interaction. Instead, mothers looked back at the baby with a blank face and didn’t move. Aghast, the babies kept trying for a while and then gave up, went limp and turned away. More startlingly, when the mothers were told to engage again, the babies refused, at first, to pay attention. They just didn’t trust someone who ignored the rules of engagement, even for a minute. Psychologist J. Kiley Hamlin and colleagues of Yale University recently showed 6- to 10-month old babies various social situations using triangles, squares and circles that play acted helping or hindering each other. The babies clearly disliked the objects that didn't help out. The psychologists concluded that babies are good judges of character, even when they're not directly involved in the action. This research is a surprise because no one thought babies were paying that much attention to the acts of others. And no one realized baby judgments were so harsh. Apparently, we were fooled into thinking babies were social dunces by their sneaky ways. Human babies, with their wobbly heads and unfocused stares, look like they aren't paying attention to much of anything. So remember, the baby is watching. That spaced-out look on her face might not be the start of a nap but the very moment in which she is deciding if you, in particular, are trustworthy. Meredith F. Small is an anthropologist at Cornell University. She is also the author of "Our Babies, Ourselves; How Biology and Culture Shape the Way We Parent" (link) and "The Culture of Our Discontent; Beyond the Medical Model of Mental Illness" (link).