If you’ve ever spent time watching chimps at the zoo, you’ve probably wondered: what are they thinking? Well, the answer might be simple: could be they’re fixin’ to hurl a rock at your head.

One chimp in Sweden actually hides stones and other potential projectiles, and then acts casual before chucking them at visitors—behavior that suggests an unprecedented degree of primate planning and deception. His duplicity is described in the journal Public Library of Science ONE. [Mathias Osvath and Elin Karvonen, "Spontaneous Innovation for Future Deception in a Male Chimpanzee"]

The chimp, named Santino, had long been known to fling things at annoying onlookers. For years he’s calmly gathered stones and chunks of concrete, stacking them in piles, which he visits when some human particularly irks him.

But lately Santino has gotten more cunning. For one, he’s taken to concealing his arsenal beneath little heaps of hay that he carries out from his enclosure. And his attacks are also more stealthy. Santino used to pitch a fit before pitching a stone. But now he acts all nonchalant, even thoughtfully munching an apple before letting the missiles fly.

The researchers say the data show that chimps are capable of social planning and deception. Unless, of course, that’s just what the chimps want us to think.

—Karen Hopkin

[The above text is a transcript of this podcast.]