Mammals sleep to preserve their energy and recover physical and mental energy. The amount of sleep a mammal needs hinges on many factors, including environment, body size, diet, age, and the safety of its sleep place. Whether animals settle on land or sea can also influence how much sleep it requires. Different mammals spend various amounts of time in non-REM sleep and REM sleep. However, all mammals examined exhibit signs of REM sleep, suggesting that mammals dream as humans do. Talking about mammalian sleep is often classified as monophasic or polyphasic. Monophasic sleep represents animals who get their sleep in one concentrated period. For instance, humans are monophasic sleepers. Our circadian rhythms stimulate us to sleep for prolonged periods at night and be active and alert during the daytime. Polyphasic sleepers have a rest for multiple periods throughout a 24-hour cycle. Polyphasic sleep is familiar, as many animals must keep caution against predators. However, if dangers ar