A basic form of ESP testing. It uses a deck of cards (such as regular playing cards or Zener cards) and repeated rounds of testing. This technique can be used to test for precognition, by having the subject guess a card before it is revealed, telepathy, by having the subject guess a card being looked at by the tester, etc.
Readers, please enjoy this guest blog post by Sandra Kynes, author of several books, including The Herb Gardener's Essential Guide, Plant Magic, and the new Witches' Encyclopedia of Magical Plants, among many others.
Although a few old books...