Editing Snake (section)

=== Locomotion ===
The lack of limbs does not impede the movement of snakes. They have developed several different modes of locomotion to deal with particular environments. Unlike the gaits of limbed animals, which form a continuum, each mode of snake locomotion is discrete and distinct from the others; transitions between modes are abrupt.{{sfn|Cogger|Zweifel|1992|p=175}}<ref name = "Gray">{{cite journal |vauthors=Gray J |title=The mechanism of locomotion in snakes |journal=The Journal of Experimental Biology |volume=23 |issue=2 |pages=101–20 |date=December 1946 |doi=10.1242/jeb.23.2.101 |pmid=20281580|bibcode=1946JExpB..23..101G }}</ref>

==== 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}}

==== Sidewinding ====
{{Main|Sidewinding}}
[[File:Neonate sidewinder sidewinding with tracks unlabeled.jpg|thumb|right|A neonate sidewinder rattlesnake (''[[Crotalus cerastes]]'') sidewinding]]
Most often employed by colubroid snakes ([[colubrids]], [[elapids]], and [[Viperidae|vipers]]) when the snake must move in an environment that lacks irregularities to push against (rendering lateral undulation impossible), such as a slick mud flat, or a sand dune, sidewinding is a modified form of lateral undulation in which all of the body segments oriented in one direction remain in contact with the ground, while the other segments are lifted up, resulting in a peculiar "rolling" motion.{{sfn|Cogger|Zweifel|1992|p=177}}<ref name = "Jayne2">{{Cite journal |vauthors=Jayne BC |title=Kinematics of terrestrial snake locomotion |journal=[[Copeia]] |year=1986 |pages=915–927 |doi=10.2307/1445288 |volume=1986 |issue=4 |jstor=1445288}}</ref> The sidewinder moves forward by throwing a loop of itself and then pulling itself up by it. By lowering its head the snake gets leverage, straightening itself out and pressing itself against the ground, it brings itself forward and at an angle that leaves it ready for the next jump. The head and the loop are in effect the two feet upon which the snake walks. The snake's body, appearing roughly perpendicular to its direction, may bewilder the observer, since preconception may lead one to associate snake movement with a head that leads and a body that follows. It appears the sidewinder is going sideways - but precisely where the snake is going, where it wants to go, the head gives clear indication. The snake leaves behind a trail that looks like a series of hooks one after the next. Snakes can move backwards to retreat from an enemy, though they normally do not.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}} This mode of locomotion overcomes the slippery nature of sand or mud by pushing off with only static portions on the body, thereby minimizing slipping.{{sfn|Cogger|Zweifel|1992|p=177}} The static nature of the contact points can be shown from the tracks of a sidewinding snake, which show each belly scale imprint, without any smearing. This mode of locomotion has very low caloric cost, less than {{frac|1|3}} of the cost for a lizard to move the same distance.<ref name="Walton"/> Contrary to popular belief, there is no evidence that sidewinding is associated with the sand being hot.{{sfn|Cogger|Zweifel|1992|p=177}}

==== Concertina ====
{{Main|Concertina movement}}
When push-points are absent, but there is not enough space to use sidewinding because of lateral constraints, such as in tunnels, snakes rely on concertina locomotion.{{sfn|Cogger|Zweifel|1992|p=175}}<ref name = "Jayne2"/> In this mode, the snake braces the posterior portion of its body against the tunnel wall while the front of the snake extends and straightens.{{sfn|Cogger|Zweifel|1992|p=177}} The front portion then flexes and forms an anchor point, and the posterior is straightened and pulled forwards. This mode of locomotion is slow and very demanding, up to seven times the cost of laterally undulating over the same distance.<ref name="Walton"/> This high cost is due to the repeated stops and starts of portions of the body as well as the necessity of using active muscular effort to brace against the tunnel walls.{{Citation needed|date=November 2024}}

==== Arboreal ====
[[File:Golden tree snake.jpg|thumb|left|[[Golden tree snake]] climbing a flower]]
The movement of snakes in arboreal habitats has only recently been studied.<ref name = "Astley">{{cite journal |vauthors = Astley HC, Jayne BC |title=Effects of perch diameter and incline on the kinematics, performance and modes of arboreal locomotion of corn snakes (Elaphe guttata) |journal=The Journal of Experimental Biology |volume=210 |issue=Pt 21 |pages=3862–72 |date=November 2007 |pmid=17951427 |doi=10.1242/jeb.009050 |s2cid=18129284 |doi-access=|bibcode=2007JExpB.210.3862A }}</ref> While on tree branches, snakes use several modes of locomotion depending on species and bark texture.<ref name="Astley"/> In general, snakes will use a modified form of concertina locomotion on smooth branches, but will laterally undulate if contact points are available.<ref name="Astley"/> Snakes move faster on small branches and when contact points are present, in contrast to limbed animals, which do better on large branches with little 'clutter'.<ref name="Astley"/>

Gliding snakes (''[[Chrysopelea]]'') of Southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees.{{sfn|Cogger|Zweifel|1992|p=177}}{{sfn|Freiberg|Walls|1984|p=135}}<ref>{{cite journal |vauthors=Socha JJ |title=Gliding flight in the paradise tree snake |journal=[[Nature (journal)|Nature]] |volume=418 |issue=6898 |pages=603–4 |date=August 2002 |pmid=12167849 |doi=10.1038/418603a |bibcode=2002Natur.418..603S |s2cid=4424131}}</ref> These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.{{sfn|Cogger|Zweifel|1992|p=177}}{{sfn|Freiberg|Walls|1984|p=135}}

==== Rectilinear ====
{{Main|Rectilinear locomotion}}
The slowest mode of snake locomotion is rectilinear locomotion, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning.{{sfn|Cogger|Zweifel|1992|p=176}} In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. Waves of movement and stasis pass posteriorly, resulting in a series of ripples in the skin.{{sfn|Cogger|Zweifel|1992|p=176}} The ribs of the snake do not move in this mode of locomotion and this method is most often used by large [[Pythonidae|python]]s, [[Boidae|boa]]s, and [[Viperidae|viper]]s when stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.{{sfn|Cogger|Zweifel|1992|p=177}}