"Claudio: Now you talk of a sheet of paper, I remember a pretty jest your daughter told us of.
Leonato: O, when she had writ it and was reading it over, she found Benedick and Beatrice between the sheet.
The word sheet is used to refer to a piece of paper and used to refer to a bed sheet, with an innuendo placed in between about Beatrice and Benedick.
From Act 1, sc. 1, when Benedick and Beatrice are exchanging insults, one example of a pun is: "What my dear Lady Disdain! Are you yet living?" spoken by Benedick to Beatrice. He uses the word "disdain" both as a name for Beatrice and as a description of her attitude toward him. She shows him scorn, or disdain.
Much Ado About Nothing is a classic Shakespearean comedy, and vast amount of puns, or play on words, can be found all throughout the play.
A pun can be found in the opening scene when Beatrice refers to Benedick as "Signior Mountanto" (Act 1, Scene 1). Mountanto refers to "montanto," which is a term associated in fencing to an upward thrust. Beatrice is implying, therefore, that Benedick has bad fencing skills.