Bit between the teeth

To take the bit between one’s teeth means to take control of a situation with resolution and determination. This is odd in the sense that if a horse takes the bit between its teeth, it cannot be controlled. The bit is the piece of metal attached to the reins and is located at the back of the horse’s mouth behind its teeth. By pulling or relaxing the reins, the bit exerts or releases pressure on the back of the horse’s mouth, giving the rider full control of the horse’s movements. If, for some reason, the horse dislodges the bit from the back of its mouth and takes it between the teeth, the horse cannot be controlled. The expression has been used in its figurative sense since the mid-1600s.