Sleep in Animals

Cattle, horses, and sheep are unique in that they can sleep while standing, though none may experience REM sleep in this position, for REM sleep causes partial muscle paralysis. For REM sleep to take place, the animals must lie down. Conversely, birds may have periods of REM sleep while perched. Some breeds of dogs usually sleep throughout the day like cats, while other breeds have only one daily sleep session. While dreaming, dogs may make a quiet barking sound while both cats and dogs may make running motions with their legs.