It's the language that it's put in. The english back then was way different than it is now.
Memories can be elusive, but so can escape for a prisoner. The title of a book can elude you, too, if you're trying to remember it.
Gulper eel has a mouth so big it can swallow the Atlantic hagfish.
Discord, Jealousy, Pride.
The reader has direct access to the inner thoughts and feelings of Poe's narrator but not those of Mr. Hyde.