Fly traps and mouse traps are both trigger traps designed to catch something. The fact it was able to evolve without there being any sort of "intermediate" plant still around today is somewhat of a mystery. Additionally, the plant is so easy to kill you wonder how it was able to evolve and survive at all.
I actually had a two fly traps, one that I bought in November a year ago that recently died because I never hibernated it, and another that didn't get watered for 3 weeks because the coworker who said they would do it while I was gone on xmas break didn't. That one is slowly on a death spiral, still alive but on its way out.