Boa constrictors have a pretty cool (or terrifying) trick up their sleeve.
They can tell when its prey's heart has stopped beating.
When it comes to all the different ways nature has cooked up for an animal to kill its prey, constricting is one of the most energy inefficient.
Imagine flexing every muscle in your body as hard as you can until someone dies. Sounds exhausting.
Well it is REALLY exhausting, so it helps the boa to know when they can stop squeezing so as not to waste any energy.
Researchers found this out by simulating heart beats in rat cadavers and they noticed the snakes always let go shortly after they shut off the heartbeat.
So if you ever get attacked by a boa, all you have to do is stop your heart until they let go, then restart it and run away before it starts eating you.
[Image courtesy Wikipedia.]