nothing ,but if you want be safe you should get a safty mat
Step1
safety mat
First, if you want to be safe you should get a safety mat.
Step2
You have to point both of your feet forward. Then put 1 hand down then the other and you have to keep your arms strait then you have to put all you momentum in to it. (if you want allot of momentum have a running start)
Step3
upside down
You have to go upside down and you should land in the same stance that you started with and facing the way you came from.
Step4
You have to practice allot if you want to start off easy you should go slowly and not throw your feet above you head but to the side then after a while you just go higher and higher.
Tips & Warnings
Practice allot and to start go slow
You should use a soft place to practice
Be careful of rocks and shells etc.
Don't do a cart wheel on a hard surface unless you have to