Click source for video -> http://www.nytimes.com/2015/08/24/scienc....html?_r=0
Quote:It’s pretty obvious that boa constrictors squeeze the life out of their prey.
But how, exactly? Do they suffocate them?
That explanation, long the conventional wisdom, had been challenged but not tested, according to Scott M. Boback, a herpetologist at Dickinson College in Pennsylvania.
He joined with his colleague Charles F. Zwemer and several undergraduates to do just that. Their conclusion, reported in The Journal of Experimental Biology, is that blocking blood flow — not stopping the breath — is what kills the prey.
For anyone who studies snakes, the evolution of constriction is important. This method of killing appeared very early among snakes, and it also evolved independently among different snakes. Dr. Boback said that snakes called black racers, common in the Southeast, are constrictors, but evolved separately from boas, and more recently.
He and his colleagues were already studying constriction. “We had a system set up,” he said, so they decided to take on the problem, using an anesthetized rat as prey. First they implanted heart and blood pressure sensors in the rat — delicate instruments and a delicate procedure — then subjected them to a violent test.
“The snake doesn’t care that you put all these things into the rat,” Dr. Boback said. “He strikes out and rips this thing out of your hand.”
The researchers took blood samples from the rat immediately before and after the test.
The results were unmistakable. Within six seconds after the snake enveloped the rat, Dr. Boback said, the rat’s arterial blood pressure dropped by half. Its heart rhythms started going haywire. And the blood tests showed changes like potassium shooting up to dangerous levels.
In addition, blood oxygen saturation did not drop to the levels that would be expected if the rat was suffocating.
Any one of the effects the researchers observed could be fatal, Dr. Boback said, which suggests how efficient constriction is, and perhaps why it has been so important in the evolution of snakes.