Most people think constrictors like boas and anacondas squeeze the air out of their prey with their muscular coils. And most people are wrong, according to a new study that offers an entirely different theory. Dickinson College researcher Scott Boback explains that colleague Dave Hardy first noticed two decades ago that the speed at which prey die in the clutches of a boa is far too quick to be from suffocation—a painful, drawn-out process, per a release. He supposed an animal's death was caused by circulatory or cardiac arrest, says Boback, but there were no studies to back him up. Twenty years later, Boback says his study in the Journal of Experimental Biology proves Hardy was right: Boas cut off prey's blood flow to the heart, brain, and other vital organs by closing blood vessels and sending pressure in the arteries plummeting. The animals pass out in seconds and die relatively quickly, researchers say.
It wasn’t pleasant work coming to that conclusion. Researchers anesthetized 24 rats, put ECG electrodes and vascular catheters into their bodies to monitor heart rate and blood pressure, then watched as they were squeezed by nine boa constrictors, reports Smithsonian. After six seconds, a rat's blood circulation dropped by half. "I remember being in the room and the students were looking at the data in disbelief that it happened that fast," says Boback. The oxygen supply was eliminated within the next minute as the rat's heartbeat began to falter. After six minutes, more than 90% of the rats had died, likely from irreparable heart damage as their veins were crushed, though they were probably unconscious from the first seconds, Boback says. "The heart literally doesn't have enough strength to push against the pressure," he tells National Geographic. Boback adds snakes' quick crushing skills probably evolved to protect them from prey with sharp teeth and claws. (Snakes once had ankles.)