How a Snake Can Raise its Neck High although its Body is Very Soft. Similarity with a Thin Plastic Tube Filled with Air

TL;DR

This study reveals how king cobras can raise their heads higher than expected by controlling internal air pressure, effectively stiffening their bodies, which provides insights into the mechanical properties of slender animals.

Contribution

It demonstrates that snakes can actively control their body stiffness through internal air pressure, a novel finding linking biological control to mechanical properties.

Findings

Snake head height can be increased by controlling internal air pressure.

Effective elastic modulus correlates with neck height via a scaling law.

Force or constriction pressure is proportional to snake diameter.

Abstract

The bodies of snakes, such as king cobras, are very soft so that it is nearly impossible for them to raise their heads higher than around one meter. By direct measurement, we were only possible to hold the body of a freshly killed cobra vertically at around 0.05 m. Here, for the first time it is reported that the king cobra can control the effective elastic modulus of its body so that it can raise its head up to several tens of centimeters. The effective elastic modulus is enhanced by increasing the pressure of air trapped inside the respiration channel, which is similar to increasing the stiffness of a thin plastic tube by filling it with air at pressure above atmospheric pressure. The neck height increases with the effective elastic modulus according to a scaling relationship. It was also simply proved that the peak of force or constriction pressure is proportional to the snakes diameter. This work may provide a physical foundation underlying the mechanical properties of slender animals.