Video Extras

The Ghost Experiment
Chimps that watch how other chimps retrieve a grape from a trick box can pick up the skill. But researcher Lydia Hopper wanted to see whether chimps could learn the same skill after seeing the trick box opened by a ghostly, invisible thread.

An Indirect Approach
In this short outtake, primatologist Brian Hare tests whether a bonobo can figure out how to get an apple slice precariously perched on a window sill.