bite down

Verb

 * 1)  To bite (something) very hard and usually for a purpose (like to hold it in one's mouth).
 * Biting down on my wallet, I had two hands free to open the door.
 * 1)  To clench with one's teeth.
 * He bit down to force himself not to say anything.
 * 1)  To repress or bite back an (emotion, impulse or reaction).
 * She bit down on the urge to strike the woman who had wronged her.