Editing Snake (section)

==== Lateral undulation ====
{{Main|Undulatory locomotion}}
[[File:Foot prints of Snake.jpg|thumb|Crawling prints of a snake]]
Lateral undulation is the sole mode of aquatic locomotion, and the most common mode of terrestrial locomotion.<ref name = "Gray"/> In this mode, the body of the snake alternately flexes to the left and right, resulting in a series of rearward-moving "waves".{{sfn|Cogger|Zweifel|1992|p=175}} While this movement appears rapid, snakes have rarely been documented moving faster than two body-lengths per second, often much less.<ref name = "Hekrotte">{{Cite journal |last=Hekrotte |first=Carlton |name-list-style=vanc |title = Relations of Body Temperature, Size, and Crawling Speed of the Common Garter Snake, Thamnophis s. sirtalis |journal=[[Copeia]] |year=1967 |volume=23 |issue=4 |pages=759–763 |doi=10.2307/1441886 |jstor=1441886}}</ref> This mode of movement has the same net cost of transport (calories burned per meter moved) as running in lizards of the same mass.<ref name = "Walton">{{cite journal |vauthors=Walton M, Jayne BC, Bennet AF |title=The energetic cost of limbless locomotion |journal=[[Science (journal)|Science]] |volume=249 |issue=4968 |pages=524–7 |date=August 1990 |pmid=17735283 |doi=10.1126/science.249.4968.524 |bibcode=1990Sci...249..524W |s2cid=17065200}}</ref>

Terrestrial lateral undulation is the most common mode of terrestrial locomotion for most snake species.{{sfn|Cogger|Zweifel|1992|p=175}} In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc.{{sfn|Cogger|Zweifel|1992|p=175}} Each of these environmental objects, in turn, generates a reaction force directed forward and towards the midline of the snake, resulting in forward thrust while the lateral components cancel out.<ref name = "Gray_lissman"/> The speed of this movement depends upon the density of push-points in the environment, with a medium density of about 8{{clarify|What does this refer to? What scale?|date=June 2016}} along the snake's length being ideal.<ref name = "Hekrotte"/> The wave speed is precisely the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it, allowing snakes to move through very dense vegetation and small openings.<ref name="Gray_lissman">{{cite journal |last1=Gray |first1=J. |last2=Lissmann |first2=H. W. |title=The Kinetics of Locomotion of the Grass-Snake |journal=Journal of Experimental Biology |date=February 1950 |volume=26 |issue=4 |pages=354–367 |doi=10.1242/jeb.26.4.354 |bibcode=1950JExpB..26..354G }}</ref>

When swimming, the waves become larger as they move down the snake's body, and the wave travels backwards faster than the snake moves forwards.<ref name = "Gray2">{{Cite journal |vauthors=Gray J |title=Undulatory propulsion |journal=[[Quarterly Journal of Microscopical Science]] |year=1953 |volume=94 |pages=551–578}}</ref> Thrust is generated by pushing their body against the water, resulting in the observed slip. In spite of overall similarities, studies show that the pattern of muscle activation is different in aquatic versus terrestrial lateral undulation, which justifies calling them separate modes.<ref name = "Jayne1">{{cite journal |vauthors=Jayne BC |title=Muscular mechanisms of snake locomotion: an electromyographic study of lateral undulation of the Florida banded water snake (Nerodia fasciata) and the yellow rat snake (Elaphe obsoleta) |journal=[[Journal of Morphology]] |volume=197 |issue=2 |pages=159–81 |date=August 1988 |pmid=3184194 |doi=10.1002/jmor.1051970204 |s2cid=25729192}}</ref> All snakes can laterally undulate forward (with backward-moving waves), but only sea snakes have been observed reversing the motion (moving backwards with forward-moving waves).{{sfn|Cogger|Zweifel|1992|p=175}}