The sloth.
-Sloths move only when necessary and even then very slowly; they have about a quarter as much muscle tissue as other animals of similar weight. They can move at a marginally higher speed if they are in immediate danger from a predator (4 m or 13 ft per minute for the three-toed sloth), but they burn large amounts of energy doing so.
-As much as two-thirds of a well-fed sloth's body weight consists of the contents of its stomach, and the digestive process can take a month or more to complete. Leaves, their main food source, provide very little energy or nutrients, and do not digest easily. Since leaves provide little energy, sloths deal with this by a range of economy measures: they have very low metabolic rates (less than half of that expected for a mammal of their size).
There. You learned something today.