In 1994, a rogue herpetologist challenged the dogma that constricting snakes kill by suffocation. He didn’t think it made sense. If suffocation were the mechanism, the prey would have died much more slowly—minutes rather than seconds. Instead, he thought the immense pressure from the snake’s contorted body sent its prey into cardiac arrest. It has taken 20 years, but researchers have finally proved him right. To test the idea, a physiologist and ecologist set up an experiment that recorded the heart rate and blood pressure of a mouse trapped in the coils of a boa constrictor (snake pictured above). They knocked the mouse out, hooked it up to electrodes and catheters, and then made the offering to the lab’s hungry snake. The researchers watched as the snake bit, contorted, and wound its prey into a deathly corkscrewlike grip. The results, published online today in The Journal of Experimental Biology, showed that in just 6 seconds, the rodent’s blood pressure plummeted, and its heart rate shot up. This cardiac chaos and cutoff of circulation (not a lack of air) was the main mechanism that killed the mouse. The constriction also caused potassium levels in the mouse’s blood to skyrocket, an effect that, on its own, could cause major cardiac issues, even death by heart attack. But because the enormous pressure from the snake cuts off circulation in the mouse, it’s likely that the potassium-rich blood doesn’t reach the whole body. Researchers think elevated, constriction-induced potassium levels may work as a sort of back-up plan for the snake, so that if the prey does somehow escape, and blood begins to recirculate, the animal is still doomed, its blood now toxic.