Explanation: King Henry II of England was so enraged by the behavior of Archbishop Thomas Becket that he, supposedly, chewed on the carpet in a fit of pique.
It's also (rarely used now, I think? though I remember it being a 'crap past the radar' gag in a cartoon in my youth) slang ('carpet eating' or 'munching') for performing oral sex on a woman, so poor Henry's wife is getting a false positive here.