You can teach your dog to lie down. But you can't teach him to lie, or to know when you're lying. Because a new report shows that Spot can't spot deception. The study's in the journal Behavioural Processes. We've all known pooches who run and hide when their owners shout "let's go for a ride"—when what they really mean is "we have an appointment with the vet." But do the dogs really know that their people are being duplicitous? To find out, Mark Petter, a student in clinical psychology at Dalhousie University in Canada, decided to fib to some Fidos. In his experiment, dogs were shown two covered containers. One held a treat. The other: nothing but disappointment. In half the trials, a helpful trainer stood behind and pointed to the container holding the treat. In the other half, a deceptive trainer pointed to the empty container. The results? The dogs approached the honest trainer a little more often than they did the deceiver. But not enough to conclude that the pups had figured out that one of the guys was pulling their leg. So dogs may be able to sniff out bombs. But they can't pick up the smell of mendacity.