When Benedick is lured into believing that the lady, Beatrice, loves him, it is when he is hiding and listening to two men of his own social station (or higher), the Count Claudio and Don Pedro, and a relative of Beatrice (her uncle Leonato) talk. Claudio and Pedro both know that Benedick is hiding within earshot, and they have rehearsed what they say to trick him. Before they speak so that Benedick can hear, they compare Benedick to a kid fox (II.iii.39) (an Elizabethan term for a crafty young man). Here is what they say to trick Benedick:
DON PEDRO: How, how, I pray you? You amaze me. I would
have thought her spirit had been invincible against all
assaults of affection.(110)
[Aside] I should think this a gull but that the
white-bearded fellow speaks it. Knavery cannot, sure,
hide himself in such reverence.(115)
I would have sworn it had, my lord—especially
In this scene, they continue the animal imagery, comparing Benedick now to a fish (104) taking bait. Two things that are particularly convincing to Benedick are that a man of eminence, older than himself or his companions (Leonato) speaks this, so it must be the truth, and that all three of the conspirators believe that Benedick will immediately scorn Beatrice's sincere and heartfelt love. Benedick, who is a man who respects authority, but is also somewhat contrary by nature, is fully caught by these twin prongs of the argument. The final straw is that the "truth of this [is] from Hero", as the Count, Leonato, and Don Pedro say. Benedick, being a chivalrous man, is unwilling to believe that a lady such as Hero would lie. The trick would not work, however, if Benedick had not already feelings for Beatrice; this deception provides the impetus for him to take action.
Beatrice's gulling scene is similar in many ways. Two women of Beatrice's social level "catch" her while she is hiding in the same arbor that Benedick did, talking about Benedick's love for Beatrice. Again, the fish imagery is used (III.i.26) by Ursula and Hero to describe Beatrice. Ursula and Hero talk of Benedick's worthiness (as the men in II.iii talk about Beatrice's worthiness), but Hero says that she will counsel Benedick to be still about his (reputed) love for Beatrice. But Beatrice, they say, will only scorn him, and he does not deserve it. The format of both "gulls" is essentially the same. At the end of the scene, the women use another animal image, now that of a songbird "limed" (105) -- that is, caught.
The differences in the scenes are significant, however. The gulling scene for Benedick is longer, and involves three speakers rather than two. This implies that Benedick, being a man of strong character, may need more convincing than a woman. Beatrice's scene, which is shorter and less convincing, is aimed more at shaming Beatrice out of her scorn; Benedick's scene does involve that, it's true, but it also involves a much more vivid scene evoking pity for the "lovelorn" Beatrice. The mode of secrecy, too is different. In Benedick's scene, the reason Beatrice will not proclaim her love is that she is proud, and has ever, before, scorned him. In Beatrice's scene, however, Benedick is to be told to keep his love to himself. This is more believable, presumably, because a man in this era would be required to do the wooing, whereas a woman would be more likely to wait quietly.