The ability to occlude the thumb is the key to the magic trick, so the thumb must be opposable. Garcia-Pelegrain and colleagues replaced the coin with morsels of food: ...

Monkeys without opposable thumbs aren’t fooled by magic tricks, study finds By attempting sleight-of-hand magic tricks on monkeys, scientists learned some interesting things about cognition ...

The magic trick requires an opposable thumb, and the idea here was to test “whether having the manual capability to produce an action, such as holding an item between finger and thumb, ...