Crazy about ESP

In 1961 when I was a Freshman, one of the guys in the dorm became almost
religiously convinced that ESP, specifically telepathy, was genuine. 

He wanted to show this by picking pairs of subjects from among his dorm
mates.  The "sender" would draw a playing card from a deck and
concentrate on it while the "receiver" would sit in the next room and
try to divine the identity of the card.  

The rest of us decided to give him a run for his money.  I rigged a little telegraph consisting of a
battery, a flashlight bulb for the receiver, and a key made from two
little metal strips taped at one end to a wood insulator and projecting
beyond it so that they could be squeezed together to make contact.   
Since the other guys didn't know Morse, I devised a simple code where
the first series of "dots" indicated the suit while the second gave the
value of the card within that suit. 

Needless to say, the "telepathy" was amazingly successful.  Even when the receiver did not get the card right, he was generally off by only one bit, for example calling a 9 an 8, or a diamond a heart.  We strung this believer along for several days before revealing the source of the "magic."