Sharks can sense the tiniest of movements — muscles twitching, nerve cells firing. That’s because they can actually sense their prey’s electricity field. (They use electroreceptors, or, as the BBC calls them, “jelly-filled pores on their heads.”) This electric-sensing head-jelly superpower is why it’s so hard to escape a shark. They’re gonna get you. They can feel you out there.
And one type of baby shark — brownbanded bamboo shark embryos still in their egg cases — can also use that sense to escape predators with another power: playing dead. Ed Yong explains at National Geographic:
When they sensed fields that match the breathing of a nearby predator, they quickly froze. They even kept their gills still, effectively holding their breath as long as they could. And they coiled their tail around their bodies in a little still ball.
It’s probably the cutest thing you’ll ever see a shark do, although it’s important to remember that these babies are developing the senses that will turn them into extremely effective killers as adults.
Shark embryos 'freeze' to evade predators, BBC News.