You’re eating apples with your friend Dr. Psychic Psycho, a talented biochemist who fancies himself a clairvoyant and has made many accurate oddball predictions.

“I have interesting news for you,” he says. “You must seriously consider taking this pill. As you know (since we have recently determined it together), it contains substance X, which (as you also know — but consult this pharmacopeia if in doubt) is fatally poisonous by itself, while nevertheless furnishing unfailing antidote to poison Z — though it does have some minorly unpleasant side effects. Now the apple I gave to you, which you have just finished eating, was poisoned by me with Z — or not — in line with my prediction as to your taking or not taking the antidote pill. Benign old me, of course, only poisoned the apple if I foresaw that you were indeed going to take the antidote. And not to worry — I’m a very good predictor.”

He rushes off. What should you do?

(By University of Pittsburgh philosopher Nicholas Rescher.)