When Helen visits Sherlock's office to ask for his help, she recounts the events of her sister's passing in disturbing detail. In particular, she uses a simile to describe her sister's altered physical condition upon her death:
By the light of the corridor-lamp I saw my sister appear at the opening, her face blanched with terror, her hands groping for help, her whole figure swaying to and fro like that of a drunkard.
Helen paints a horrifying picture here, which contributes to the ominous mood of the story. Curiously, Helen compares her sister's body movements, "swaying to and fro," to that of a "drunkard." This simile suggests that some external force has deprived her sister of control over her own body. It also alludes to the fact that, like a drunkard, her sister is intoxicated. Later, when readers learn that Dr. Roylott's murder weapon was the venom of his swamp adder, the basis of this simile becomes clear: Helen's sister was "drunk" with the adder's poison. In this way, Doyle's use of simile not only heightens the reader's fear and apprehension, but also offers a clue that might help the reader solve the crime.
