That riddle is sometimes called "criminal cupbearers". Common presentation uses 1000, gives it away to use a power of two. A really fun extension to it is to

That riddle is sometimes called "criminal cupbearers". Common presentation uses 1000, gives it away to use a power of two. A really fun extension to it is to suppose that you use the same criteria (a thousand bottles, consumption of the smallest amount will kill, but after a delay that means you must perform a one-pass test) but _two_ bottles are poisoned. What is the minimum number of prisoners you need for your test to find the two poisoned bottles precisely and what is the procedure? (This is _substantially_ harder.)