Boa constrictor snakes are famous for squeezing the life out of their prey, but how do they avoid accidentally cutting off their own air supply while crushing something to death? If growing a baby can interfere with human lung function, how exactly are snakes able to have entire corpses in the food tubes without suffocating?

New research has found the answer: boas can control their ribs to moderate where the air goes in and out. The findings, published in the Journal of Experimental Biology, go some way towards explaining how these snakes continue accessing oxygen while preparing their meal – though exactly how they do it is still something of a mystery.

“The neuromuscular control of this behavior is still unclear,” corresponding author John Capano from Brown University told IFLScience.

“We do however know that at least boas, and likely most snakes, are able to control very discrete sections of ribs and recruit just a few ribs within the over 200 pairs along their body.”

Being crushed to death takes time, and it’d hardly be an effective hunting strategy if the predator went the same way as the prey, so it seemed reasonable to assume there was an adaptation that enabled the snakes to keep breathing rather than simply holding their breath. To see what this might look like, Capano and colleagues popped a blood pressure cuff around boa constrictors' ribs to mimic rib compression.

Their approach revealed that when compressed, the boas could use lower lung sections (further from the head of the snake) like bellows to pull air in when rib action wasn’t an option. This means that if the front half of the body is busy squeezing the air out of a rabbit, the lower lungs can act as a backup for the ribs while they’re out of action.

Snake lungs are long, extending in boas across a third of their length, but they can stretch up to 80 percent of the snake’s body depending on the species, says Capano. However, gas exchange only takes place in the frontmost regions, while the balloon-like later sections are mostly needed for shifting air.

Another surprising find was that the rib motion of boas was very similar to that seen in monitor lizards. While the two are considered to be cousins, Capano says the molecular data currently suggest monitors are most closely related to iguanas, so this was “very cool to find”.

Deadly and fascinating, but the team behind the paper certainly had to work for their conclusions.

“Snakes can be hard to work with because they are so flexible and move in such different ways than other animals,” Capano explained.

“This makes it very hard to connect them to equipment with wires, because they easily get snagged on just about everything. They are also a little bit intimidating, as they will strike, hiss, and constrict to defend themselves, so you just need to gauge each snake's temperature and behavior as you work.”

Next, they hope to explore if or how locomotion affects breathing for snakes, as it’s currently unclear if the rib movement involved in this could impede breathing or indeed stop it altogether.