Editing Concertina movement (section)

=== Tunnel ===

{{distinguish|tunnel snakes}}

Tunnel concertina locomotion is often employed in unobstructed tunnels, where the snake lacks both sufficient contact points to perform lateral undulation and sufficient lateral room to perform sidewinding.<ref name="Jayne2" />  During tunnel concertina locomotion, the snake anchors itself by flexing its body in a series on alternating bends which press against the walls of the tunnel. The snake extends the anterior portion of its body by straightening these bends, then flexes the anterior portion of the body to form anterior anchor points while pulling the posterior portion forward. This mode of concertina, while still slower than lateral undulation or sidewinding, is still fairly fast, with snakes moving approximately 10% of their length per second.<ref name="Jayne2" /> However, because the snake is straightening and re-forming bends, it requires the entire space of the tunnel to move, and any obstruction will disrupt locomotion.  In the presence of either of these, snakes will switch from concertina to another mode (as both of the above are faster and more economical), though in the case of extreme lateral constraint (tunnel width less than 3x body width), snakes will ignore the contact points that could be used in lateral undulation and perform concertina.