It is like "under one's breath."Hello! I would like to know the meaning of the idiom to mutter between one's teeth. Couldn't you give some examples, as well?
Background:In the face of a looming storm, Maxwell, William and Elizabeth settled in a rundown barn close to the battlefield of Waterloo in 1815. They had been working on a plan to change the course of the battle by preventing Duke Wellington from using a monster battalion that would wreak havoc on the country's future. Maxwell had never intended to include Elizabeth in the plan, as he thought it'd be too dangerous for a girl. Being a feisty girl who was ready to take on the challenge, Elizabeth insisted on her involvement in the execution of the plan. What frustrated Maxwell more was that her friend William was on her side on this one.