| Quote #1
A monstrous shadow of him crouched upon the wall and mocked his action as he poured and drank. (11)
This is the very first instance of a "suggestive shadow" in the story. Not only is the shadow "monstrous," but the description of it as "mocking" the man with the shade (it’s his shadow) almost makes it seem independent of him. Even this early in the story, the narrator’s imagination is already starting to take on a life of its own. (Of course, a description like this also adds to the general ambience of creepiness for the reader.)
| Quote #2
I must confess that the oddness of these three old pensioners in whose charge her ladyship had left the castle, and the deep-toned, old-fashioned furniture of the housekeeper's room in which they foregathered, affected me in spite of my efforts to keep myself at a matter-of-fact phase… Their very existence was spectral; the cut of their clothing, fashions born in dead brains. (28)
A contrast between the narrator’s "matter-of-fact" phase and his more "fanciful" imaginings about the "spectral" old people. The narrator thinks reality is straightforward, clear-cut, and not mysterious or suggestive. In his book, anything mysterious or suggestive must be a product of the human imagination, as all "supernatural" things are. But the narrator’s imagination turns the old custodians into something suggestive – they become almost ghostly ("spectral") themselves.
| Quote #3
I came to the landing and stopped there for a moment, listening to a rustling that I fancied I heard; then, satisfied of the absolute silence, I pushed open the baize-covered door and stood in the corridor. (28)
This is next instance of the narrator perceiving something suggestive, which may not be there. This could be read as more evidence that his imagination is acting up at this point. It’s also worth noting that in this case the narrator thinks he hears something; most of the other perceptions are visual and not auditory.