The term "subvocalizer" refers to a person who moves their lips and tongue as if speaking, but does not actually produce any audible sound. Some synonyms for this term include "mumbler," "whisperer," and "talker under one's breath." Other similar terms include "mutterer," "mutterer to oneself," and "silent speaker." These terms are often used to describe someone who is deep in thought and muttering to themselves, or someone who is trying to communicate without being heard by others. Overall, the use of synonyms for "subvocalizer" can be helpful in clarifying and describing the behavior of someone who communicates through non-audible vocalization.