Blue-spotted Lagoon Ray

Rays can sense the electric pulses given off by the heartbeat of a crab and will sweep over the sand looking for them. In one experiment they hooked up a lie detector test to a crab and passed a shadow over the top of it and found that the crab’s heart rate slowed down. Crabs can slow down their heart rate to weaken the electric signal and to escape detection by the stingray.
More importantly, crabs can fool a lie detector test.
Guardian: Jarrod Weidner