Mouthing a speech makes me think of a baby, chewing bread, gumming it, really, since he has not teeth yet. It’s like taking a text and turning it into mush. Except that mouthing also calls to mind an overarticulation, a wrapping one’s mouth around words wider than one needs to – like someone fake biting instead of actually sinking your teeth into it – the way we pretend to eat the hands and feet of children we find adorable.
And now, of course, mouthing has come to mean saying something without voice, without sound, moving one’s lips and teeth and tongue in the shape of words but never voicing them – which is surely not what Hamlet means here – but does have the rather charming quality of somehow connecting up all these ideas into one funny mouthing idea.