I was at a magic show, when after one particularly amazing trick, someone screamed out, "wow, how did you do that." I would tell you", answered the magician predictably, "but then I'd have to kill you." After a moments pause the same voice screamed out "can you tell my mother in law?"
A physics teacher writes a question on a board:
"A 40 kg child that 100 cm tall is holding a parent's arms swinging them 0.5 revolutions a second. If the parent let go of the child after 2 seconds, where will the child end up?"
A few moments later, the teacher then comes over and reads a student's answer: