Request a member of the company (seated) to place a shilling or florin
upon each knee, and cover them with his hands with his fingers stretched
out. You then tell him, when you turn your back, to raise one of the
coins and tap his head with it twelve times just above his ear; then
replace it on his knee and cover it with his hands as before; and you
will tell him, on examining the coins, which one he raised.
The examination of the coins has really nothing to do with the trick.
All you have to do is to look at the person's hands; the blood leaves
the hand that has been raised, and when it is again placed beside the
other the difference in colour is most perceptible.
I have performed this trick hundreds of times in drawing-rooms, and it
has never been detected, but created great surprise.