It is diurnal . Many species hold their heads erect on their long necks, which gives them the appearance of being alert. They intimidate predators by lashing out with their tails, inflating their throats, hissing loudly, turning sideways, and compressing their bodies. They are mostly terrestrial, but many are agile climbers and good swimmers. The tail is somewhat compressed in tree dwellers, very compressed in semiaquatic monitors.
Monitors threaten by opening the mouth, inflating the neck and hissing.
The ribs may spread, flattening the top of the body, or the body may just expand slightly. This makes the monitor look larger than it actually is. It often raises up on its hind legs just before attacking. The tail delivers a well-aimed blow. Monitors tend to swallow their prey whole, like snakes.