Guys & Lucy ..... A limerick has specific rhythm that has to be adhered to. Allow me to attempt to rearrange rovers masterpiece (though non-limerick) to demonstrate my point.
Ahem *cough*
There once was a young lassie from trim
Who's arse I was gagging to rim
I nearly started go cum
When she lowered her bum
Later on I moved on to her quim.
Notice lines 1,2 & 5 rhyme and have the same number of beats. lines 3 & 4 should also rhyme. this is a limerick. Hope this demonstrates it for you guys and Lucy.