The phenomenon of return or re-excitation is a phenomenon that occurs in the brain of humans and animals when the nervous system returns to a previously known environment and sensations begin to arise again, although a lot of time has passed. Research shows that it is during the period of sleep or weak awakening that the body is most susceptible to repeated entries into an already familiar environment. This can manifest itself as a feeling of freshness and fullness even after a short rest, as well as an increased sense of smell after being indoors. It is believed that this ability was an evolutionary advantage, as it made it possible to maintain life in conditions of constant stress.