Sloths are famous for their unusual and bizarre bathroom habits. Both two-fingered (Choloepus) and three-fingered (Bradypus) sloths will only defecate once a week, and for some strange reason they will only do it on the ground. For a sloth, this is a big deal. A sloths entire lifestyle is based around avoiding detection and using as little energy as possible. It takes a sloth an entire month to digest just one leaf, meaning that they don’t have much wiggle room when it comes to expending energy. Descending from the safety of the canopy to the forest floor is not only energetically very costly, it is also a suicide mission. Sloths are extremely vulnerable to predation when on the ground. As if that isn’t enough, these animals can store up to a third of their body weight in faeces; lugging that extra weight around is no easy task when you are a sloth. So why bother? There must be a huge selective advantage to this weird weekly routine – it should be obvious. Yet this remains one of the biggest mysteries surrounding sloth behaviour and one that scientists have struggled to explain for decades.