The Venus flytrap Dionaea muscipula is a carnivorous plant that ensnares and digests animal prey, particularly insects and spiders. The trap is sprung when an unfortunate insect brushes against two of the touch-sensitive hairs on the leaf surface within about 20 seconds of each other.
Stretch receptors in the base of the hairs then trigger an electrical signal that spreads across the leaf, causing the cells on the underside of the lobes to expand rapidly (it is still not known whether they take on water or change the shape of their cell walls).
When open, the lobes curl outwards at the edges. But the swelling cells cause the lobes to buckle inwards and snap shut. Though the plant has evolved to digest insects, larger strains have occasionally been found to contain the skeletons of small frogs.