I read some time back that Ken Kesey (author of One Flew Over the Cuckoo's Nest, among other things) took part in some of the early tests of LSD. One of the things that the doctors doing the testing wanted to find out was how the drug affected the drugged's sense of time. They would do it by asking the subject to sit quietly, and then announce whenhe/she thought a minute had elapsed.

Well, Kesey knew the rate of his pulse, so he'd put his hand on his wrist, sit quietly counting, and repeatedly say "Now" at exactly one minute. Good trick, that.