Alone, Benedick talks to himself about how Claudio has changed since his engagement to Hero. Benedick has lost a good friend since Claudio now thinks of nothing but Hero and their approaching wedding. He ponders what perfect combination of qualities a woman must possess before he himself would marry her.
When Benedick hears Claudio, Leonato, and Don Pedro approaching, he hides in the arbor to eavesdrop/note what they say.
Don Pedro and the others know that Benedick has hidden himself within the sound of their voices. Don Pedro asks the musician Balthasar to sing for them, and he sings a song that begins, "Sigh no more, ladies, sigh no more. Men were deceivers ever."
After the singer leaves, Don Pedro, Claudio, and Leonato converse loudly about how much Beatrice really loves Benedick in spite of the way she treats him. She will not show affection toward him for fear that she will be rejected. They agree not to speak of it to Benedick for now, and they leave.
Benedick can scarcely believe what he has heard, but because Leonato was part of the group, he does not think it can be a joke. He admits that he did not plan to marry and has been contemptuous of marriage, but maybe he can change for the sake of Beatrice. In fact, he suddenly realizes she has all those qualities he was enumerating earlier.
Beatrice reluctantly approaches Benedick to call him for dinner. When he tries to speak kindly to her, she replies unkindly and leaves. He tries to read love into her words and reaffirms to himself that he must try to love her.
This scene is the first of two contrived overhearing/noting scenes in Don Pedro's plan to bring Beatrice and Benedick together. Benedick does not perceive that they have set him up; instead, he eavesdrops/notes the contrived conversation about Beatrice and her love for him and believes it all. The next scene — Act III, Scene 1 — is a parallel scene in which Beatrice overhears/notes a conversation about Benedick's love for her.
Benedick is first suspicious that this is a "gull" — a hoax cooked up by his friends — but Leonato, "the white-bearded fellow speaks it: knavery cannot sure hide himself in such reverence." Therefore, Benedick is inclined to believe what they say about Beatrice's love for him. Benedick's complete change of heart about marriage and about Beatrice is obvious in the comparison of his two monologues — before and after his eavesdropping — from his easy talk about the perfection he requires in a woman, to his admission that he "will be horribly in love with her." He recognizes that he is going against his reputation, and others may make fun of him when they find out. But he accepts the fact that he has a right to change his mind:
. . . doth not the appetite alter? A man loves the meat in his
youth, that he cannot endure in his age.
He appears to move toward loving and being loved with relief first and then with eagerness.
When Beatrice suddenly comes to call Benedick to dinner, he interprets even her insults as veiled expressions of affection. She, of course, has not yet been subjected to the planned eavesdropping/noting treatment by her friends (which will take place in the next scene).