In the opening paragraph, the narrator describes how powerful his senses have become.
The disease had sharpened my senses—not destroyed—not dulled them. Above all was the sense of hearing acute. I heard all things in the heaven and in the earth. I heard many things in hell.
Although there is little or no mention to the senses of taste or smell, the sense of touch is evident. His touch is light and careful. He prepares carefully each night for a week in the hope of killing the old man, taking an hour to slowly open the door.
And every night, about midnight, I turned the latch of his door and opened it—oh so gently! And then, when I had made an opening sufficient for my head, I put in a dark lantern, all closed, closed, that no light shone out...
I undid the lantern cautiously—oh, so cautiously—cautiously (for the hinges creaked)—I undid it just so much that a single thin ray fell upon the vulture eye.
But he cannot kill the man until he can see the open eye. These actions, both the snail's pace of his movements and his unwillingness to commit the act until all is right, help to create a sense of terror and suspense. His later physical action is one of gruesome madness.
I dismembered the corpse. I cut off the head and the arms and the legs.