This is a fun rhyme to do as it involves falling backwards from a seated position. (Great ab workout!)
Begin by establishing a beat (clapping, tapping on knees, stomping, etc.)
I had a mule.
His name was Jack.
I rode his tail
To save his back.
His tail fell off
And I fell back!
Whoa, Jack!!!! (On this line fall backwards)
Repeat, perhaps changing the way you establish the beat.