I clicked for the topic, but it was the writing that captured me.
The first impulse sets a secret timer, and what the fly does in the next 20 seconds will determine its fate. If it avoids the hairs, it will live. If it bumps a second one, it sets off another electrical impulse, which raises the trap’s calcium levels above a critical threshold. The plant responds by sending water into its leaves, which rapidly change shape from convex (bent outwards) to concave (bent inwards).In other words, the trap snaps shut. —The Atlantic