get 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 gets the bit between her teeth, she's the best student in my class.

If you get the bit between your teeth, you become very enthusiastic and determined about doing a particular task. Note: In the first and third expressions, a `bit' is a piece of metal which is held in a horse's mouth by the bridle and reins. You're persistent when you get the bit between your teeth, I'll say that for you. Note: You can also say that someone has the bit between their teeth or has got the bit between their teeth. It's going to be difficult against Leeds United but the lads have got the bit between their teeth. Others sense that the prime minister has the bit between his teeth and believe that action will follow. Note: The bit should be put at the back of a horse's mouth, behind its back teeth. When a horse bolts (= runs away very fast), it sometimes takes the bit between its teeth, which makes it very difficult for a rider or driver to use the reins to control it.