Sloths are among the slowest animals in the world – plus they snooze for about 15 hours a day – and this is reflected in their metabolism. Spending most of their lives hanging upside down, sloths feed mostly on the fibrous leaves, fruits and sap of certain trees, and their digestion is so slow that, when full, their stomachs can account for 37% of their body mass. They are also 'picky poopers', often making a very slow descent all the way down to the ground to relieve themselves.