You may have heard about the suggestion of “playing dead” if you ever encounter a brown bear in the wild—and surely would not hope to prove the effectiveness of the tactic by yourself. In the natural world, feigning death is the survival technique for many species.
Most predators instinctively avoid consuming dead animals—they are aware of the toxins present as bacteria digest a carcass over time. Feigning death is a tactic evolved in a number of prey. Some will freeze their activities and play dead to evade predators. Scientists have observed such practices in many snake species when confronted with predators. However, the strategy may not work in the eyes of predators with a higher cognitive ability—they can still distinguish whether the motionless creature is “fresh” or not.
In theory, feigning death works best when there are swarms of prey at the scene. Predators would try to capture the most prey within the shortest time. To lower the opportunity cost, the predator targets live prey instead of checking out every carcass, hence the apparently dead ones survive.
Apart from being a psychological trick, feigning death can also act as physical defence. Scientists have found that Pygmy grasshoppers (Criotettix japonicus) stretch out their hind limbs and back plate when threatened by frogs, which, without teeth to crush the prey, find the exaggerated death pose difficult to swallow. The frog will have to give up on the challenging prey.
Meanwhile, it is not only prey species that resort to the immobility strategy; some predators employ the same tactic to capture their prey. Adult fish known as Livingston's cichlids (Haplochromis livingstoni), for example, often lie flat and stay on lake beds for a long period, in an attempt to lure small fish to come forward and become their meal!