Zoology , giraffes sleep standing up with one eye open and both ears moving.
While a giraffe may only sleep for minutes at a time, the little brown bat typically sleeps 12 to 19 hours without stopping. They are nocturnal creatures, which means they sleep during the day and are awake at night. Bats spend most of the day hanging upside down in small, dark crevices or with claws hooked into ceilings. Have you ever wondered why they sleep upside down? A Cornell University guide to bats notes it is because their wings are not strong enough to fly into the air from the ground. It is more efficient for bats to use gravity by dropping into flight from their perch.
Have you ever seen a sleeping squirrel? Most likely not because the most common squirrels, such as the grey squirrel, are tree dwelling, according to the Ohio Department of Natural Resources . This means that they make their homes high up in trees or attics. Squirrels sleep in nests called dreys that look a lot like birds' nests. They use twigs, leaves, moss, bark, grass, paper and even dog hair to build their homes. In the winter, several squirrels will cuddle together in the drey for warmth.