1.1.162: Claudio talks with Benedick about his new-found fascination with Hero. Claudio also introduces one of the central motifs in the play: the task of "noting" (or looking on and making an observation about something). Claudio asks if Benedick "noted" Hero, and then goes on to gush about how he found Hero to be a modest young lady. It’s notable that in this conversation, Claudio announces he thinks Hero is the sweetest lady he ever saw, after he says he’s noted her modesty. (Modesty seems pretty important to him).
1.1.195: Claudio announces that though he’d sworn against marriage in the past, he’s willing to take back that oath now if Hero will have him.
1.1.223: Claudio now chats with Don Pedro about his feelings for Hero. He hears Don Pedro praise Hero, and suggests that Don Pedro might be trying to draw him into loving Hero, by not giving his honest opinion of the girl. Still, Claudio says he speaks his true thoughts when he says loves Hero.
1.1.296: Claudio asks if Leonato has any sons and then goes on to explain to Don Pedro that he "looked upon" Hero before they went to battle, but he was busy with the war, then. Now, Claudio says "soft and delicate" desires are taking the place of "war-thoughts." The aforementioned desires are prompting him to think he loved Hero before she went off to war.
1.1.312: Claudio worries that his love for Hero might seem too sudden, and wishes he could put a better face on it by talking about it for longer.
2.1.162: Claudio lies to Don John (who is also lying to Claudio). Don John knows that the masked man he's speaking to is Claudio, but asks if he’s Benedick. Claudio lies and says he is Benedick (playing into the first of Don John’s many traps).
2.1.167: Claudio asks Don John for proof that Don Pedro loves Hero, and is satisfied when Don John asserts that he heard Don Pedro admit his love for Hero.
2.1.172: Claudio says that he’s now certain of Don John’s news. (Remember he asked that one question, and then was like, "It must be true! Don John says so!"?) Anyway, Claudio signs off on his love for Hero after declaring that friendship (meaning his friendship with Don Pedro) can be relied on in all things, except love. He also calls beauty a "witch" that can inspire even faithful friends to obey their passions over their duty to their friends.
2.1.193: Benedick teases Claudio about Don Pedro stealing Hero, and Claudio says that he hopes Don Pedro finds joy in Hero. (Way to stand up for your girl, ace.) As Benedick continues to jest, Claudio swoons around, and when he can’t get Benedick to go away, he simply leaves himself.
2.1.290: Faced with Don Pedro (who he thinks has stolen Hero) Claudio doesn’t admit to Don Pedro that he’s upset at all. Instead, Don Pedro has to prod him for what’s wrong. Still, Claudio won’t admit what’s bothering him.
2.1.306: Claudio leaves it up to Don Pedro to clear everything up, and thankfully Don Pedro does. Claudio says he is too overjoyed to speak, now that he’s gotten Hero. He says he gives himself over to her as much as she gives herself over to him.
2.1.357: Claudio is ready to go to church tomorrow, as time goes slowly until love gets all its "rites." Leonato’s like, "Hold on there, soldier boy."
2.1.373: Claudio agrees to aid Don Pedro in his scheme to get Benedick and Beatrice together.
2.3.92: Claudio and Don Pedro hold a conversation within earshot of Benedick, who is hiding. The two men concoct a story for Benedick to overhear how much Beatrice loves Benedick. Claudio seems gleeful in his manipulation. He delights in bawdy jokes about the two and then lays it on thick about Beatrice’s personal agony in this whole "loving Benedick" affair. Claudio praises Benedick some, though he does say he thinks Benedick will only torment Beatrice if he learns of her love.
3.2.3: Claudio offers to escort Don Pedro home. Claudio then gives over to teasing Benedick, who’s looking pale with love. Claudio jokes about the signs that Benedick is in love, and rubs it in that some woman loves him in spite of knowing him, and all of his faults.
3.2.76: Claudio seems happy to think that their scheming will bring Benedick and Beatrice together after all.
3.2.117: Claudio seems shocked at Don John’s statement that Hero is disloyal, but he doesn’t interrogate Don John thoroughly. Instead, he says "Who, Hero?" and "Disloyal?" and "May this be so?" He doesn’t exactly demand that Don John support this dangerous claim with any substantive evidence.
3.2.123: Without any real investigation, Claudio comes to the passionate conclusion that if he sees anything at Hero’s window that suggests he shouldn’t marry the girl, he’ll disgrace her in front of the whole congregation gathered to see them wed. (It’s not the most sensitive plan, but Claudio’s pride is wounded at the suggestion that his girl could be unfaithful.)
4.1.23: At his wedding day, Claudio is a drama queen. Rather than come right out with it and say Hero is disloyal and he won’t marry her, he questions everyone about whether they know any good reason why he shouldn’t marry Hero. He even asks Leonato what he could possibly give in return for such a noble gift as Leonato’s daughter. Claudio really hams it up here.
4.1.29: Claudio denounces Hero publicly as knowing "the heat of a luxurious bed." He says all her blushing is from guilt, not from modesty. He declares they’ve all been tricked to ignore her real sinfulness by her cunning outward appearances. Also, he calls her a rotten orange, which is not so nice.
4.1.48: Claudio talks to Leonato, who thinks maybe Claudio believes Hero is a ‘round the way. Leonato assumes that Hero gave up her virginity to Claudio, thinking of him as a husband already. Claudio insists that this isn’t the case, as he was completely honorable in his affections to her, like a brother to a sister, before they were wed.
4.1.56: When Hero tries to defend herself, Claudio insists that what she seemed to be doesn’t matter. He declares he thought of her like Diana, goddess of the virgins, when actually was like Venus, goddess of the not-at-all virgins.
4.1.73: After Claudio’s already made a big to-do about Hero’s guilt, he gives her the chance to defend herself, supposedly. He claims she’s the only one who can stain her own virtue, and then he asks her who she was talking to out of her window the night before.
4.1.100: After Hero simply says she didn’t talk to anyone, Don John and Don Pedro go off on long speeches about how she’s a liar and a harlot. Claudio wishes the girl farewell, and laments that she wasn’t what seemed to be. Finally, he claims he’ll never look so gently on love again, and all beauty will become thoughts of harm.
5.1.52: Leonato and Antonio face Claudio. Hearing that Leonato is wronged, Claudio asks, "Who wrongs him?" The obvious answer seems to be that Claudio wronged him, what with killing his child and ruining his family’s name.
5.1.55: Claudio continues to insist that he won’t fight Antonio or Leonato, and is surprised at Leonato’s charge that Claudio is a villain. Rather than deal with the men reasonably (or respectfully), Claudio haughtily dismisses them.
5.1.122: Claudio sees Benedick, who seems to be in a pretty bad mood. There’s some more back and forth, and Claudio teases that Benedick’s wit is dull, without realizing Benedick’s wit is sheathed because his sword is out, and he’s looking to sink it into Claudio.
5.1.151: Hearing Benedick’s serious challenge, Claudio is light in his reply. He says he’ll meet Benedick "so I may have good cheer," which literally means "so long as I may have good cheer," but also might mean that it would please Claudio to challenge Benedick. Either way, Claudio is too glib in his dealing with this serious charge.
5.1.154: Claudio goes on to tell Don Pedro that Benedick has accused him of being an idiot, guising the charge with wordplay about feasts. Claudio continues to tease Benedick, and joins Don Pedro in joking about how Benedick will soon wear the cuckold’s horns of a married man.
5.1.195: After Benedick leaves, Don Pedro notes the man was "in earnest." Claudio, to show that he couldn’t possibly take Benedick’s accusations of villainy seriously, says Benedick is indeed earnest…earnestly in love with Beatrice. Claudio continues to be full of jokes until Borachio shows up and explains that Claudio has been made a fool by Don John.
5.1.246: Claudio is shocked at Borachio’s news, saying he had "drunk poison" while Borachio gave his speech.
5.1.251: Claudio says Hero now appears in his mind’s eye just as unstained as the first day he loved her.
5.1.271: Claudio says he doesn’t know how to ask for Leonato’s patience, but he’ll suffer any revenge Leonato devises for Claudio’s sin. Then Claudio immediately backtracks, saying he didn’t actually sin, unless it’s a sin to make a mistake.
5.1.292: Claudio cries. He’s really glad Leonato is being so nice to him, and agrees to marry Leonato’s mystery niece, and also to go put an epitaph on Hero’s tomb this evening.
5.1.329: Claudio’s all, "Tonight I’ll mourn with Hero."
5.3.3: Claudio reads the epitaph written for Hero. The epitaph admits that though Hero was slandered to her death, now that she’s been cleared, her reputation will live on. Claudio promises that he’ll return every year to Hero’s grave and perform this ritual.
5.3.32: Claudio sends everyone on their way, and announces that he hopes this wedding goes better than his last wedding, which was kind of a wreck.
5.4.37: Claudio commits to marrying whatever woman Leonato puts before him, even if she is "an Ethiope."
5.4.62: Claudio’s shocked when he sees Hero again, and declares, "Woah, another Hero!" except he actually doesn’t say "woah."
5.4.85: Claudio doesn’t say another word about his this whole marriage affair, never mind a "Sorry I killed you that one time, Hero." Instead, he teases Benedick by revealing a paper he found with a love poem from Benedick to Beatrice.
5.4.112: Claudio’s last lines in the play are teasing Benedick. Claudio says he had hoped that Benedick would have denied Beatrice, in which case he could’ve gotten Benedick to marry some other woman, and become a cheating husband. He adds, Benedick will no doubt be a cheating man anyway, if Beatrice doesn’t keep too close an eye on him.