In Shakespeare's Romeo and Juliet, what are four literary devices used in Act III, Scene 1?
Since formatting limits the length of answers, I had to shorten your question to refer to only one Act. Also, scenes 2 through 5 of Act III have already been analyzed for literary devices in previous questions, therefore I focused on Act III, Scene 1.
Two similes can be found in this scene:
1) Mercutio tells Benvolio: "Thou art as hot a Jack in thy mood as any in Italy." This is a simile comparing Benvolio's temper to the fiery temper characteristic of Italians. The name Jack is being used similar to how we would use John Doe to represent any average person. Hence Mercutio is saying Benvolio's temper is as aggressive as anyone's in Italy.
2) Mercutio: "Thy head is full of quarrels as an egg is full of meat." Mercutio is comparing Benvolio's head to that of an egg, saying that his head is as densely packed with arguments as an egg is densely packed with protein.
Assonance, the repetition of vowel sounds can be found in Mercutio's line: "What eye but such an eye would spy out such a quarrel." This line repeats the long vowel sound "i."
A pun, or play on words can be found in Tybalt's and Mercutio's exchange. Tybalt says: "Mercutio, thou consort'st with Romeo,--"
Mercutio responds: "Consort! what, dost though make us minstrels?"
Tybalt is using consort to refer to companionship or association, while Mercutio translates it by its musical definition, referring to a group of instrumentalists or singers performing together.
Alliteration can be seen in the phrase: "fire-eyed fury." The "f" consonants are repeated at the beginning two words near each other.
Mercutio uses personification when he asks Tybalt, "Will you pluck your sword out of his pilcher by the ears? Make haste, lest mine be about your ears ere it be out" (3.1.81-83). He gives the human attribute of possessing ears to Tybalt's sword, asking Tybalt, essentially, to draw his sword from its "pilch," or scabbard, so that they can fight. The second sentence of the quotation employs some wordplay: Mercutio tells Tybalt to draw his sword out by its "ears" quickly otherwise Mercutio will have his own sword at Tybalt's ears before Tybalt is even ready.
When Mercutio describes the wound Tybalt has inflicted upon him, he says it is "a scratch, a scratch" (3.1.97). Here, he employs understatement; it is a great deal more than a scratch as he admits a moment later that it will be "enough" to kill him.
Mercutio uses similes when he describes the wound to Romeo: "'tis not so deep as a well, nor so wide as a church door [...]" (3.1.100-101). Here, he compares the size of the wound's opening to the depth of a well and the width of a church door, saying that it is not as deep or wide, respectively, but it is at least deep and wide enough to kill him.
Finally, Mercutio uses a pun when he tells his friend, "Ask for me tomorrow, and you shall find me a grave man" (3.1.101-102). Grave can mean "serious," but it also refers to the place where we would bury a body. Mercutio's wound is quite serious -- it will kill him -- and so both meanings work in his sentence. It is clever, if sad.