Mutter makes your character mutter to someone. If the command is directed to a certain person, all people in the room will see you mutter to this person, and the person in question will see you mutter to them.
EXAMPLES
"mutter"You: You mutter. Anybody: Hotblack mutters."mutter to marvin"You: You mutter to Marvin. Marvin: Hotblack mutters to you. Anybody: Hotblack mutters to Marvin.