How does Shakespeare's simile in Mercutio's lines 22-24 found in Act 3, Scene 1 contribute to developing the mood of the scene in Romeo and Juliet ?
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. (III.i.22-24)
The simile found in Mercutio's speech to Benviolio in the scene in which Mercutio is killed helps to portray the tense mood in this scene due to its use of irony.
The tension in the mood of this scene is clearly expressed in Benvolio's opening lines as he begs Mercutio to get off the street, warning that:
The day is hot, the capulet's abroad.
And if we meet, we shall not scape a brawl,
For now, these hot days, is the mad blood stirring. (III.i.2-4)
However, Mercutio shifts the mood to a slightly humorous mood by not paying attention to Benvolio's warning and instead replying with his characteristic wit. We can especially see irony in Mercutio's simile describing Benvolio's temper and his tendency to quarrel because in actuality Mercutio is describing himself, not Benvolio. We know Benvolio to be a very level-headed character and a peacemaker. Just like Mercutio's name symbolically suggests, it is Mercutio who has the hot, easily provoked temper. The name Mercutio represents mercury, which is the most easily changeable metal, especially when heat is applied to it.
We see Mercutio using his simile to describe Benvolio's temper when he says, "Thy head is as full of quarrels as an egg is full of meat" (22-23). In this simile, the term "meat" refers to the yoke of an egg. In other words, Mercutio is saying that Benvolio is as full of the desire to quarrel, or fight, as an egg is full of yoke, which is of course ironic because Benvolio is the peace lover, the one begging Mercutio to get off the streets. Mercutio continues his ironic simile to say that Benvolio has been hit so many times for picking fights that his brains are now as scrambled as an egg, which we see in the lines, "...and yet thy head hath been beaten as addle as an egg for quarrelling" (23-24).
However, Mercutio's speech, including the simile, does more than just add ironic humor. It makes the reader sense that Mercutio is about to do something very stupid. If Mercutio is as likely to quarrel as Mercutio is describing Benvolio to be, then his speech is foreshadowing Mercutio's upcoming, foolish mistake.
Hence, Mercutio's simile adds irony, but it also adds to the tense mood of the scene by foreshadowing Mercutio's upcoming foolish mistake.