Two players, both either using their left hands or their right hands, hold hands by hooking their four fingers together and closing their hands into fists with their thumbs pointing up to the ceiling.
Both players say the following chant together and for each word said, tap your thumb on alternating sides of your interlocked fist.
One, Two, Three, Four
I declare a thumb war!
While still holding hands, try to pin your opponents thumb down to the fist. Once pinned, count to three out loud. If they remained pinned until the count is finished, you’ve won!
See the following video for an adorable demonstration.