Pirahãs take naps (fifteen minutes to two hours at the extremes) during the day and night. There is loud talking in the village all night long. Consequently, it is often very difficult for outsiders to sleep well among the Pirahãs. I believe that the Pirahãs’ advice not to sleep because there are snakes is advice that they literally follow—sleeping

Perhaps most intriguing, REM sleep helps us maintain our emotional awareness. When we are deprived of REM, studies have found, we have a more difficult time reading others’ facial expressions.