This knave gooth hym up ful sturdily,
And at the chambre dore whil that he stood,
He cride and knokked as that he were wood.

– Geoffrey Chaucer

The Canterbury Tales, The Miller’s Tale. The servant yells and knocks on Nicholas’s door like a madman – "as if he were wood." This foreshadows the madness that John believes he sees in Nicholas, and later when Nicholas and Alison tell the townspeople that John is mad.