system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we "shush" people to try to quiet them?
gpt
The "S" sound is very high frequency, so is easier to place in three dimensional space. The purpose of "Shush" is to draw attention to your face, so that you can convey to the noisy person your displeasure in their conduct (via the means of a stern gaze).

The need for a high frequency sound is so that you can do this without yourself creating much noise and becoming an offender, and subsequently shushed by someone else.