Sharks can sense the tiny electric field your beating heart gives off
Clusters of jelly-filled pores on a shark's snout, called the ampullae of Lorenzini, can detect electric fields as faint as five billionths of a volt per centimetre, sensitive enough to pick up the electrical signal of a prey animal's muscle twitches hidden under sand. It's precise enough that a shark can find a flatfish buried completely out of sight using electroreception alone.