Boa constrictors don’t like to waste their hugs. A study involving dead mice and fake hearts shows that the snakes loosen their deathly grip once their prey’s pulse stops. This reaction allows the snakes to save energy.
Scientists fed sixteen wild and captive-born snakes on dead rats rigged with artificial hearts that either beat continuously, pumped for ten minutes or were still.
They warmed the rats with an electric blanket to mimic live prey, and implanted two small water-filled bladders in their chest cavity and abdomen to monitor the boas’ squeeze. The bladder in the chest cavity was placed right next to the rats’ actual heart and hooked up to a piston pump to simulate heartbeats.
The team found that the boas squeezed all rats, but would frequently adjust their hugs and periodically give a tighter squeeze if they sensed a heartbeat. Rats with no pulse were released after 10 minutes and squeezed with half the pressure of those whose heart beat continuously through the 20-minute trial. In experiments where the heartbeat was switched off halfway through, it was a matter of minutes before the snakes released their coils. Learn more here, here or here.