Durdles tells Jasper that he was drunk and asleep in the crypt,
last Christmas Eve, and was wakened by "the ghost of one terrific
shriek, followed by the ghost of the howl of a dog, a long dismal,
woeful howl, such as a dog gives when a person's dead." Durdles
has made inquiries and, as no one else heard the shriek and the
howl, he calls these sounds "ghosts."

They are obviously meant to be understood as supranormal
premonitory sounds; of the nature of second sight, or rather of
second hearing. Forster gives examples of Dickens's tendency to
believe in such premonitions: Dickens had himself a curious
premonitory dream. He considerably overdid the premonitory
business in his otherwise excellent story, The Signalman, or so it
seems to a student of these things. The shriek and howl heard by
Durdles are to be repeated, we see, in real life, later, on a
Christmas Eve. The question is--when? More probably NOT on the
Christmas Eve just imminent, when Edwin is to vanish, but, on the
Christmas Eve following, when Jasper is to be unmasked.

All this while, and later, Jasper examines Durdles very closely,
studying the effects on him of the drugged drink. When they reach
the top of the tower, Jasper closely contemplates "that stillest
part of it" (the landscape) "which the Cathedral overshadows; but
he contemplates Durdles quite as curiously."

There is a motive for the scrutiny in either case. Jasper examines
the part of the precincts in the shadow of the Cathedral, because
he wishes to assure himself that it is lonely enough for his later
undescribed but easily guessed proceedings in this night of
mystery. He will have much to do that could not brook witnesses,