Some of the funniest brain teasers trick people into answering them incorrectly. One example states that Jill's mother has three children and that the oldest are named May and June. When asked the name of the third child, many say "July" when the actual answer is "Jill."
Similar brain teasers rely on people's own biases and misconceptions regarding the question. One classic example tells the story of a young man in an accident that kills his father. When he arrives at the hospital, Dr. Smith says, "I can't operate on this boy; he's my son." When asked how this answer is possible, many people are stumped because they assume Dr. Smith is a man. The real answer is simple – Dr. Smith is the boy's mother.
Other funny brain teasers rely on wordplay or make use of other knowledge that an individual needs to have to answer the question. The question "When is four half of five?" may seem like an impossible question to answer. However, the solution – when it is a Roman numeral – relies on an individual knowing that the Roman numeral for four, IV, can also stand for the middle two letters of the word "five."