Thumb Wrestling

Monochrom's Massive Multiplayer Thumb-Wrestling - Explains the basics as well as multi-player variations. Includes photographs.
www.monochrom.at/daumen/netzwerk-eng.htm

Samurai Thumbs - Describes how to play this game using helmeted thumb wrestlers as warriors. Includes some variations.
www.deepfun.com/thumb.htm

Thumb Wrestling - Describes how to thumb wrestle, with a snake in the grass variation.
www.gameskidsplay.net/games/other_games/thumb_wrestling.htm

Wikipedia - Thumb Wrestling - Description of how the game is played.
en.wikipedia.org/wiki/Thumb_Wrestling