For those who don't know, a limerick is a five-line poem with the
rhyming scheme AABBA (the first, second, and fifth lines rhyme with one
another and the third and fourth rhyme with one another). The rhythm of
a limerick is also important, but rather than attempt to describe that
I'll recommend a site that does a better job than I would:

http://www.sfu.ca/~finley/discussion.html

-Varian

Penned by my hand on the 8th of Slyphian, in the year 110 MA.