I have lied. Since everyone lies, that must be a lie and I have told the truth. But everyone lies...oww, my head.
Captain Kirk: Harry lied to you, Norman. Everything Harry says is a lie. Remember that, Norman. *Everything* he says is a lie.
Harcourt Fenton Mudd: Now I want you to listen to me very carefully, Norman. I’m... lying.
Norman: You say you are lying, but if everything you say is a lie, then you are telling the truth, but you cannot tell the truth because you always lie... illogical! Illogical! Please explain! You are human; only humans can explain! Illogical!