A Venus flytrap does not believe the first touch. Each lobe of the trap has a few stiff trigger hairs, and brushing one sends an electrical signal through the leaf, but on its own that signal does nothing. Only if a second touch comes within about half a minute does the trap snap shut. In 2016 a team in Würzburg showed that it keeps counting after that: around five signals and the leaf starts making digestive juices. The caution makes sense. A trap can only close a handful of times in its life, and a raindrop or a falling seed touches a hair once and lies still. A fly does not lie still. So the plant waits for the one witness it can trust, which is the fly itself, testifying twice.