When describing Detective Jones to Watson (just before they meet in the bank cellar), Holmes uses a pair of similes, as seen in the following passage:
“I thought it as well to have Jones with us also. He is not a bad fellow, though an absolute imbecile in his profession. He has one positive virtue. He is as brave as a bulldog and as tenacious as a lobster if he gets his claws upon anyone.”
The similes in this passage—in which Holmes describes Jones as being “as brave as a bulldog” and also “as tenacious as a lobster”—communicate Holmes’s respect for Jones, despite the fact that he also considers the detective to be “an absolute imbecile.” Clearly, Holmes appreciates Jones’s courageous nature, even if he doesn’t respect the man’s intelligence.
This is one of the many moments in the story—and in the Sherlock Holmes series more broadly—in which Holmes’s commitment to being logical trumps his commitment to following the rules of polite society. He has logically assessed Jones’s skills (after working with the man before) and deduced that Jones has only “one positive virtue”—his tenacity. While others would avoid sharing their analysis so plainly, Holmes is quite comfortable criticizing and offending people if he sees it as an extension of rationalism and truth.
When describing to Holmes the habits of his assistant “Spaulding” (later revealed to be the criminal Clay), Wilson uses a simile, as seen in the following passage:
“Never was such a fellow for photography. Snapping away with a camera when he ought to be improving his mind, and then diving down into the cellar like a rabbit into its hole to develop his pictures. That is his main fault, but on the whole he’s a good worker.”
The simile here—in which Wilson describes Clay as “diving down into the cellar like a rabbit into its hole to develop his pictures”—captures the consistency and tenacity with which Clay hid away in the cellar of the pawnbroker’s office to “develop his photos” at odd hours during the workday.
This moment is also an example of foreshadowing because, as readers later learn, Clay was not developing photos at all, but digging a tunnel from Wilson’s office to the nearby bank in order to enter the bank from below and rob it. The simile adds to the foreshadowing as the image of a rabbit “diving […] into its hole” mirrors Clay diving into the tunnel that he was secretly digging beneath Wilson’s building. This is one of the many examples in the story of appearances not being exactly what they seem—Clay is not a simple photographer but a skilled criminal.