The Greek word translated "dumb" (NASB, kophos) refers to deaf people, mutes, and people who were both deaf and dumb. This man"s condition was the result of demonic influence, though that was not the cause in all such cases (cf. Mark 7:32-33). The crowd"s reaction here climaxes their reaction in this entire section of the text. Here was someone with more power than anyone who had ever appeared before. Messiah would heal the dumb ( Isaiah 35:5-6). The natural conclusion was that Jesus was the Messiah. [source][source][source]