Why do they bleed bill in Treasure Island book?

In "Treasure Island," the character Blind Pew delivers a "black spot" to Bill Sykes, signaling that his time is up due to his treachery and failures. This act serves as a form of pirate justice, marking Bill for retribution from his former associates. The "black spot" symbolizes judgment and serves as a catalyst for the unfolding events, ultimately leading to Bill's demise. It illustrates the brutal and unforgiving nature of pirate life.