What does Mercutio mean in Act II, scene 4, lines 16-24, of Romeo and Juliet?What does that line mean in modern english
If the line notes that eNotes's version of this use are the same that your version uses, you are talking about the lines where Mercutio is talking about Tybalt and his fencing ability. (By the way, you can use that second box to put some of the lines in to be sure we're talking about the right ones -- if you ask further questions on here.)
What Mercutio is saying is that Tybalt is a really good fencer. He is saying that Tybalt does all his fencing moves just exactly how the instruction books would tell you to do them. And he says Tybalt is really good at killing people. So he is saying that Romeo is in trouble if they fight.
Mercutio and Benvolio were talking about the fact that Romeo's father received a letter from Tybalt, a challenge on Romeo's life.
Mercutio uses the lines you mentioned to refer to the type of fighter that Tybalt is. He is well-known for his marksmanship and sword play. Mercutio likens Tybalt's perfect abilities to the beat and meter of a song. He notes Tybalt has a perfect timing to the point at which he strikes. He can strike exactly where he wants to with the precision of a butcher and he does so like a gentlemen at sport.