The sentence below (perhaps seen on a sign in a hospital) was discussed in a 1979 paper by Watson and Reich [1] and has attracted a good deal of interest in the intervening years.
What does it mean? Whoever wrote it presumably meant "Don't ignore a head injury however trivial it is", and that is what most people read it as, but if we unpick the wording carefully that is not what it literally means.
Compare it with "No citizen is too poor to be taxed" which says that no citizen is so poor as to be exempt from being taxed, i.e. all citizens are taxed. So it seems the hospital sign has a meaning opposite to the intended one.