likely, indicates that William’s mouth is hanging open as he attempts to understand Touchstone’s remarks about wise men and fools.
Shakespeare is having a bit of fun by naming the country bumpkin William. William is, of course, Shakespeare’s own first name; and Shakespeare himself came from the country. Touchstone’s rival, though, is a man of few words. He speaks short simple sentences, and he is utterly defeated by Touchstone’s blustering and excessive verbiage.
In this scene Shakespeare points out that the successful suitor and lover is a man of words. However, in this scene the words are essentially meaningless: Touchstone threatens William knowing full well that he will never have to back them up with action.
The scene is comical. Audiences will laugh at William, who believes Touchstone’s empty threats. However, the audience is also aware that Touchstone – in this scene – is like Sir John Falstaff (the fictional braggart from Shakespeare’s Henry IV plays): he is all bark and no bite. His words carry no weight. Touchstone has no real desire to engage in a physical fight with William.