Quote from : Monty Python and the Holy Grail Movie

King Arthur: Cut down a tree with a herring? It can't be done.
[the Knights of Ni scream and cover their ears]
Knight 1: Don't say that word!
King Arthur: What word?
Knight 1: I cannot tell! Suffice to say, is one of the words the Knights of Ni cannot hear!
King Arthur: How can we not say the word if you don't tell us what it is?
[the Knights of Ni scream again]
Knight 1: He said it again!
King Arthur: What,"is"?
Knight 1: No, no, not "is". Wouldn't get very far in life not saying "is".