Chewing sound is a kind of white noise, and noise is a kind of sound with uneven frequency distribution, which makes people feel very upset after listening. But white noise is the opposite, because its sound frequency distribution is relatively uniform. For example, when I was a child, my mother would sing a lullaby to put us to sleep, but not singing in time is also a very soothing lip sound.

Under normal circumstances, people's chewing sound is even and gentle. Therefore, when people are preparing to fall asleep, after hearing the sound of chewing, people's breathing will gradually become gentle, and the brain's thinking will gradually become gentle. That kind of chewing sound is like giving the listener a brain massage, and the whole person's frequency begins to be in tune with that kind of chewing sound, so after hearing the chewing sound, the whole person will slowly start to relax, so people who are slow to respond will also start to fall asleep.