The expression "an apple a day keeps the doctor away" puzzled me for a long time, because apples have very little nutritional value. But then I understood the origin: in northern climes, it's easy for an unseasonable period of bad weather to result in frozen fruit. Throwing a frozen apple at the head of one's doctor is a highly efficacious way to deter them from attempting a subsequent visit. Especially if one employs a catapult.