Have everyone lie in a circle with each other’s head’s on each other’s stomachs.
On “go”, the first person will shout “HA” and then it will be repeated one by one clock-wise around the circle. (When you do this everyone’s heads bounce up on the person’s stomachs).
Then you shout two”HA HA’s” and go around. Continue doing this and increase the number of “HA’s!”
See if you can get up to 10 HA HA’s without everyone going bananas laughing!