When Holmes and Watson find the dead body of Dr. Roylott at the end of "The Adventure of the Speckled Band," Watson says that Roylott "had a peculiar yellow band, with brownish speckles, which seemed to be bound tightly round his head." This turns out to be a snake, which Roylott had been releasing into Helen Stoner's room with the intention of poisoning her and which has now killed him instead.

Watson's description of the snake confirms the aptness of Julia Stoner's dying words. Anyone catching a glimpse of the snake would think immediately of a speckled band. In fact, Holmes identifies the creature as the swamp adder, "the deadliest snake in India." He confidently asserts that Dr. Roylott will have died within ten seconds of its bite.

Holmes confesses that the ambiguous word "band" had put him on the wrong scent for a while. There is a band of gypsies wandering the grounds of Stoke Moran, and Dr. Roylott seems to have befriended them when he showed no desire for the friendship of anyone else. He therefore thought that Julia Stoner's dying words might have referred to her murder by a band of gypsies.

This, he tells Watson, is a prime example of "how dangerous it always is to reason from insufficient data." When they arrived at Stoke Moran, Holmes's inspection of Miss Stoner's room, together with Dr. Roylott's penchant for keeping dangerous animals, quickly set him on the right track.