You may know, that I consider Gary Larson one of the all time greatest cartoonist out there. Well, consider the four pointy things at the end of the tail of the stegosaur depicted on the right, and imagine being at the receiving end of a defensive lash of said tail - not very pleasant.

Now, back in 1982 Gary Larson drew a cartoon of some cavemen in a primitive lecture hall. The man explaining stuff points to the tail of a stegosaurus and goes on "Now this end is called the thagomizer after the late Thag Simmons".

Funny stuff! Anyway, it turns out, the tail didn't have a proper name - and then it did..

http://en.wikipedia.org/wiki/Thagomizer
(also click to see the mentioned cartoon)