Limerick: A five line poem. The first, second, and fifth lines rhyme.
As in:
Consider our hero the 'Alien'
Were his forefathers really mamallian?
Or did he appear
like a fly in one's beer
from nowhere, at once, and then gone agin

(not a great example .. but you get the idea)
one line per post
Here's a starter:
"While racing in Jags at the Ring..."