All terrestrial mammals that have been examined exhibit REM sleep, which alternates with non-REM sleep, also called quiet sleep, in a regular cycle.

• 所有被研究过的陆生哺乳动物，睡觉时都会表现出REM睡眠，而且与非REM睡眠（也称为沉静睡眠）有著规律的交替周期。