I am reminded of a very silly thing we used to do as small children; it was kind of a riddle and joke all rolled into one, and it took at least 2 people in the know to tell:
Q: What's green, hangs on the wall, and whistles?
A: (gives up)
Q: A mackerel.
A: But a mackerel isn't green!
Q: So paint it green!
A: And a mackerel doesn't hang on the wall!
Q: So hang it on the wall!
A: But it doesn't whistle!
Q: So it doesn't whistle... I just put that in to make it harder.