Like all snakes, they have no eyelids and the eyes are protected by a window-clear scale called the brille. All scales tend to be smooth and shiny. The eyes tend to be small in a somewhat triangular head that is only slightly wider than the neck. Boas and pythons are powerful constrictors, but contrary to belief, do not intentionally break a victim's bones and squeeze it to a pulp. Rather, they strike with open jaws and at the same moment loop several coils around the prey, squeezing until breathing and heart action stop.
Giant boas are among the slowest of snakes.
They can be quite fast in the water. They may be slow getting from here to there but the strike is as fast as the blink of an eye. Most boas do not have the heat sensing labial pits found in the pythons, but they do have heat sensing capability. Arboreal species, specifically the green tree boas, have a series of labial pits that are infra-red heat sensors. These are depressions in or between the scales that border the mouth and vary greatly in number and structure, depending on the snake.