To do or begin doing something with decisive, independent resolve. A reference to a horse that is no longer under the rider's control because the bit (part of the apparatus used to guide it) is out of place in its mouth. You have such potential, Sophie—if you ever just took the bit in your teeth, you'd be on of the top students in this class. Rather than kowtowing to the president's public frustrations, the attorney general has taken the bit in his teeth and pressed on with the criminal investigation.