I read a review of this app (written by Steven Zuckerman, M.D.) in a medical publication, and I bought it for my son for his new iTouch. I had a bit of trouble starting it, but received a VERY prompt email reply from Greg Rostami with a VERY clear explanation - and it is fantastic! So clever and so much fun - no one so far has guessed the secret to the "magic". It really is terrific.