Boa

Both are large non-venomous constrictors from an old branch of the snakes, and they hunt in the same way, but they are separate families with consistent differences. The clearest is reproduction, since almost all boas give birth to live young while pythons lay eggs and usually coil around them to brood. Pythons also have a set of extra bones and teeth in the upper jaw that boas lack, and their heat-sensing organs sit in obvious pits in the lip scales, whereas a boa's are shallower and set between the scales. Geographically, boas are centred on the Americas with a second group in Africa and Asia, while pythons are an Old World group found in Africa, Asia, and Australia.

It depends entirely on the species. The green anaconda is the heaviest snake in the world, able to pass 5 metres and 100 kilograms, and a very large one could in theory kill and eat an adult human, though verified cases are extremely rare and the snake gains little from such risky prey. The common boa constrictor reaches 2 to 4 metres and can give a painful bite and a strong squeeze but is not considered a serious threat to a healthy adult. Most other boas are small, from half a metre to a couple of metres, and are harmless. Boa bites carry no venom, and the main risk from a big constrictor is careless handling of a large animal alone.

Almost none do. The great majority of boas are ovoviviparous, which means the female retains the eggs inside her body, where the embryos develop using their own yolk, and then gives birth to a litter of active young wrapped in thin membranes they quickly break free of. A female boa constrictor may produce 10 to 40 babies, and a large anaconda many more. Keeping the developing young inside lets the mother move them into sun or shade to control their temperature and protects them from egg predators, which may be an advantage in cooler or more seasonal climates. It is one of the traits herpetologists use to tell boas from pythons.

By constriction. The boa strikes, grips the prey with its backward-curved teeth, and immediately throws two or three coils around the body. Rather than crushing bones, it simply tightens the coils a little more each time the prey breathes out, so the chest can never re-expand. Careful studies show the animal loses consciousness within seconds and dies within a minute or two, and that the main cause is the sudden halt in blood circulation, which starves the heart and brain of oxygen, rather than slow suffocation. The boa senses the prey's heartbeat through its coils and only releases and begins to swallow once it stops.