A snake crawling on horizontal surfaces between two parallel walls exhibits a unique wave-like shape, which is different from the normal shape of a snake crawling without constraints. We propose that this intriguing system is analogous to a buckled beam under two lateral constraints. And we developed a new theoretical model based on the beam buckling to explain qualitatively the wave-like shape of the snake.

Junfeng Xiao, Xi Chen. Buckling morphology of an elastic beam between two parallel lateral constraints: implication for a snake crawling between walls. Journal of The Royal Society Interface. 2013, 10 (85).

Crawling snakes between walls with different width: the length of snakes are 61 +/- 4 cm; the radius of snake is 1 cm; the width between constraints are respectively 2 cm, 3 cm, 4 cm, 5 cm, 6 cm from top row to bottom row.