From an article by Natalie Angier in the NYTimes.com.
Frans B. M. de Waal, a professor at the Yerkes National Primate Research Center and Emory University, said chimpanzees or orangutans in captivity sometimes tried to lure human strangers over to their enclosure by holding out a piece of straw while putting on their friendliest face.
“People think, Oh, he likes me, and they approach,” Dr. de Waal said. “And before you know it, the ape has grabbed their ankle and is closing in for the bite. It’s a very dangerous situation.”
Apes wouldn’t try this on their own kind. “They know each other too well to get away with it,” Dr. de Waal said. “Holding out a straw with a sweet face is such a cheap trick, only a naïve human would fall for it.”
Apes do try to deceive one another. Chimpanzees grin when they’re nervous, and when rival adult males approach each other, they sometimes take a moment to turn away and close their grins with their hands. Similarly, should a young male be courting a female and spot the alpha male nearby, the subordinate chimpanzee will instantly try to cloak his amorous intentions by dropping his hands over his erection.
Rhesus monkeys are also artful dodgers. “There’s a long set of studies showing that the monkeys are very good at stealing from us,” said Laurie R. Santos, an associate professor of psychology at Yale University.
Reporting recently in Animal Behavior, Dr. Santos and her colleagues also showed that, after watching food being placed in two different boxes, one with merrily jingling bells on the lid and the other with bells from which the clappers had been removed, rhesus monkeys preferentially stole from the box with the silenced bells. “We’ve been hard-pressed to come up with an explanation that’s not mentalistic,” Dr. Santos said. “The monkeys have to make a generalization — I can hear these things, so they, the humans, can, too.”
One safe generalization seems to be that humans are real suckers. After dolphin trainers at the Institute for Marine Mammals Studies in Mississippi had taught the dolphins to clean the pools of trash by rewarding the mammals with a fish for every haul they brought in, one female dolphin figured out how to hide trash under a rock at the bottom of the pool and bring it up to the trainers one small piece at a time.