Flatworms fence with their penises and other fun science facts

It sounds like something out of a filthy fairy tale: the mountain tree shrew visits certain species of pitcher plant to grab a bite of nectar, and poop into the plant’s commode-shaped cup. These plants appear to have evolved so that their openings fit perfectly under the tree shrew’s behind, and they’re sturdy enough to support the animal’s weight.
It’s a crappy relationship, in the sense that the pitcher plant is actually crapped on — but the pitcher plant g