This document discusses silent sound technology, which allows people to have phone conversations without making any sounds. It works by using electromyography to detect the tiny muscle movements involved in speech and converting those signals into computer-generated audio that is transmitted to the other caller. The technology has applications for situations where sound needs to be muted, such as in meetings or for astronauts in space. However, it still faces limitations like needing electrodes attached to the face and having difficulties with tonal languages. Future improvements could make the electrodes portable and add lip-reading capabilities.