Animals have some surprising and unusual sleeping habits. For example, the giraffe only sleeps for around 2 hours a day, and does so by standing up. Sloths, on the other hand, sleep for up to 15 hours a day, and always upside down. Dolphins sleep with one half of their brain at a time, while the other half stays awake to keep them breathing. Elephants have the shortest amount of sleep of any mammal, at just 2 hours per day. These are just a few examples of the fascinating sleeping habits of animals.