Animals

Monitors swallow small prey or pieces of large prey whole rather than chew it as do iguanas and other lizards. Like snakes, they have a strong bony roof to the mouth which protects the brain from being damaged by the passage of large mouthfuls. They can also greatly increase the size of their mouth cavity by spreading the hyoid apparatus and dropping the lower jaw. Their long, deeply-slit tongue is also snakelike and is often protruded to follow olfactory “tracks". Other similarities with snakes are the shape of the vertebrae, the chamber structure of the heart, and the absence of a urinary bladder.
Powerful legs allow them to run swiftly. Long, sharp claws make them good climbers; claws also are used as tools to dig out dens or enlarge rodent dens for their own use.
When lizards walk and run, they amble from side to side, flexing their bodies laterally. The muscles that are responsible for this flexing work in a different direction to expand the chest for breathing. Thus at higher speeds flexing predominates and breathing suffers. Monitors, however. have shown no constraint on oxygen consumption because they have a throat pump. As the monitor breathes, air is drawn both into the lungs and into an expanding cavity in the throat area. The cavity contracts, pumping the air into the lungs.

Alberts, Allison. "Lessons from the Wild"