To Hannah Wood’s naked eye, it looked like the tiny spider in the pile of dead leaves in Chile wasn't doing much of anything. 

Wood, then a graduate student at the University of California, Berkeley, was in South America to study trap-jaw spiders, so named for their habit of sneaking up behind prey and rapidly snapping their mandibles shut. 

Yet at just a fraction of an inch long, the spiders themselves are hard to see, not to mention their jaws. (See "Small Spiders Have Big Brains That Spill Into Their Legs.") 

So Wood returned to the forest, took some spiders back to her lab in California, and recorded them with a high-speed video camera that records up to 40,000 frames per second. 

Playing her recordings back in super slow motion showed the secret to the spiders’ success: A rubber-band like movement that enables their jaws to move almost as fast