Dreaming sleep, which seems to be a necessity for man, may also be crucial for cats.… Scientists do not know exactly what function [REM sleep] periods serve in animals. For this reason, they call the phase paradoxical sleep.… [Researchers] have found that a group of cats deprived of paradoxical sleep for a number of days will react the same way humans do. The longer the cats were kept from paradoxical sleep, the more they tried to enter it.