Hook the four fingers of your right hand (or your left hand, if you're left-handed) with the same four fingers on your opponent's hand. If you're doing it correctly, your thumb should be pointing up towards the ceiling.
Step2
Repeat the following, "One, two, three, four, I declare a thumb war." This officially starts the thumb-wrestling competition.
Step3
Try to pin your opponent's thumb down using only your thumb, while dodging his attempts to do the same.
Step4
The game ends when you or your opponent succeeds in pinning down the other player's thumb for five seconds.
Tips & Warnings
Extend the game play by doing the best three out of five.
This is a great activity to keep kids busy on long car rides.