“What is the most interesting thing about a squirrel?” is another (to which the answer is, duh, obviously: “red squirrel or grey squirrel?”). "Microsoft and Google are known as the two companies that have historically used brain teasers in the interview process ... Candidates usually react in one of two ways. Some dismiss puzzle or estimation questions as ridiculous; others clam up under the stress of an unfamiliar question. As far-fetched as the question may sound, do take it seriously. Take a deep breath, give it your best shot." Some questions don’t actually have an answer. Full Article at Times Online