An illusion involving a hidden thumb confounds capuchin and squirrel monkeys for the same reason it does humans -- it misdirects expected outcomes of actions they can carry out. However, marmosets ...

Monkeys with hands that resemble ours fall for a sleight-of-hand magic trick, but those without opposable thumbs aren’t fooled. These differences illustrate how primates’ expectations of the actions ...

Psychologists used a sleight-of-hand trick called the French drop, in which an object appears to vanish when a spectator assumes it is taken from one hand by the hidden thumb of the other hand. The ...