There are several literary elements in Act 3.
In scene i, Mercutio begins the act by teasing Benvoilio about how easily his anger is stirred. In calling him quarrelsome, he lists the following examples of hyperbole to define Benvolio's anger:
Thou! why, thou wilt quarrel with a man that hath a hair more or a hair less in his beard than thou hast. Thou wilt quarrel with a man for cracking nuts, having no other reason but be (20) cause thou hast hazel eyes. What eye but such an eye would spy out such a quarrel? Thy head is as full of quarrels as an egg is full of meat; and yet thy head hath been beaten as addle as an egg for quarrelling. Thou hast quarrell'd with a man for coughing in the street, because he (25) hath wakened thy dog that hath lain asleep in the sun. Didst thou not fall out with a tailor for wearing his new doublet before Easter, with another for tying his new shoes with an old riband? And yet thou wilt tutor me from quarrelling!
The italicized portion is a simile.
This discussion about quarreling also foreshadows the fight that is to come later in the act.
Later in the same scene when Mercutio tries to get Tybalt to fight him, he calls Tybalt a cat, thus a metaphor emerges:
Good King of Cats, nothing but one of your nine lives. That I mean to make bold withal, and, as you shall use me hereafter, dry-beat the rest of the eight. Will you pluck your sword out of his pitcher by the ears?
After this metaphor, he personifies the sword by giving the sword the ability to have ears.