Why is 6 afraid of 7? Because 7 8 9 (7 ate 9).

Or my son's favorite way to tell it:

DS: 1 2 3 4 5 6 7 8 10
Someone older always asks: Hey, what happened to 9?
DS: 7 8 9!

Or 2 4 6 8 12 (what about 10? 6 8 10!), or 10 9 8 6 5 4..., you get the idea.