Most animals can actually survive a relatively long time without breathing: Think about drowning people who are later resuscitated, he says. But the same isn't true for a body without a heartbeat.
The team theorizes that killing by circulatory arrest has given all constricting snakes—which includes pythons and anacondas—an evolutionary advantage. The quicker the snakes can disable their prey, the lower the chance the predator will get hurt in the process.