Enticing echo

Marcgravia evenia isn’t the only sweet-sounding plant that attracts bats with an acoustic lure. In the rainforests of Costa Rica, the plant Mucuna holtonii uses a similar system, but in an even cleverer way.
 
In a newly-opened Mucuna flower, full of nectar, one of the petals is flipped up to serve as an echo reflector – signalling to the bats that it’s open for business. When a bat visits the flower, the bat sets off spring-loaded genitals that swing out – with the anthers depositing a load of pollen on the bat’s rump, and the stigma ready to pick up pollen from any other Mucuna-flowers the bat might have visited.
This action changes the reflected echo of that flower, telling other bats that it has already been visited and most if not all of its nectar is gone.