Take the bit between somebody's teeth - Idioms by The Free Dictionary
take the bit between (one's) teeth (redirected from take the bit between somebody's teeth)
take the bit between (one's) teeth
To do something decisively and with 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. Once Sophie takes the bit between her teeth, she's the best student in my class.
get/take the bit between your ˈteeth (informal) start doing something in a determined and enthusiastic way: Once he gets the bit between his teeth in an argument, no one can stop him.If the horse learns to hold the bit (see previous note) between its teeth, it can no longer be controlled by the rider.