The skylight dilemma in Martin Chuzzlewit

The house central to the murder in Dickens' Martin Chuzzlewit.  The London Walks 'Dickens and Shakespeare Literary Tour' leader told of addressing a group one day when the door of the house opened and the current owner appeared.  On asking if he had a dirty skylight the owner said, obligingly, 'yes, I do as a matter of fact, why?'