Zener Cards are used in parapsychology to determine the strength of a person's extrasensory perception (ESP) abilities. A Zener deck contains twenty-five cards: five each of a star, plus sign (cross), circle, square and a set of three wavy lines. The test requires three people: a subject, whose ability is being tested; a sender, whose thoughts the subject is to attempt to perceive; and an experimenter, who shuffles the deck in between trials. The sender takes the top card of the shuffled deck and concentrates on the symbol. The subject, who cannot see the sender, reports the card he or she believes the sender is holding. Each trial consists of going through the entire deck one time.