| An extremely poisonous substance, featured in the "battle of wits" scene in The Princess Bride. Vizzini and the Man in Black sit at opposite ends of a table, and the Man in Black claims that he has put iocaine powder in one of the two goblets of wine on the table, and gives him the option of switching them or not before they both drink from their goblets. Vizzini then uses an extremely recursive line of reasoning to decide which cup is poisoned. Watch the movie if you want to see the result.
Iocaine Powder is also the name of an algorithm that won an AI Rock-Paper-Scissors contest, using similar reasoning. | 
