The mountain tree shrew is picky about where it poops. This small mammal is found only on the island of Borneo in Southeast Asia. When nature calls, the tree shrew does its business into the bowl-shaped leaves of a Low’s pitcher plant.

Pitcher plants live on mountains at high altitudes, where soil is low in nutrients, like nitrogen. That’s why most pitcher plants are carnivorous. They get the nutrients they need to survive by trapping and eating small creatures like insects and spiders. If a bug walks on the slippery edges of one of the plants’ pitchers, it falls in. The bottom of the pitcher contains digestive juices. They break down the bug’s body, releasing nutrients that the plant absorbs. Along with bugs, Low’s pitcher plants have another nitrogen-rich food source: tree shrew poop.

This species of plant has evolved to attract tree shrews, says Jonathan Moran, a biologist at Royal Roads University in Canada. The plant has a big leaf called a lid above its pitcher. The lid oozes sweet nectar the shrews find tasty. To reach the treat, a tree shrew must position itself with its backside over the mouth of the pitcher. This opening is perfectly shaped to fit the animal’s behind. While the shrew feeds, it poops into the pitcher. Then the plant digests the droppings.

This type of relationship, in which two species benefit from each other, is called mutualism. In fact, tree shrews become protective of their chosen outhouses. They often rub their bottoms on the plants to mark their territory. “That’s why you’d never want to lick a pitcher plant,” says Moran.