Animals that have been squeezed to death by snakes probably die of circulatory arrest rather than of suffocation as was thought.

Scott Boback at Dickinson College in Carlisle, Pennsylvania, and his team anaesthetized rats and implanted probes and catheters to measure their heart rate, blood pressure and blood chemistry as the animals were being squeezed by a boa (Boa constrictor; pictured). Constriction lasted an average of 6.5 minutes, but the rats' peripheral blood pressure dropped by half as early as 6 seconds in. By the end of constriction, the rats' blood chemistry showed signs of system-wide circulatory problems and there was evidence that the heart had undergone significant electrical dysfunction.

Credit: Scott M. Boback

The authors suggest that snakes may release their prey only after detecting that it has experienced irreversible heart failure.

J. Exp. Biol. 218, 2279–2288 (2015)