The chemical is a volatile, aerosolized fear-gas developed at Baskerville (Project H.O.U.N.D.). It targets the brain’s fear centers, turning a suggestion—a "hound"—into a vivid, lethal hallucination. Sherlock’s Mind Palace reveals that "H.O.U.N.D." was an acronym for the scientists who created the gas in the 1960s. The Confrontation at the Hollow
Sherlock, initially dismissive, is hooked when Henry mentions "hound"—a word that triggers a strange flicker in Sherlock's own mind. The Beast of Baskerville [S2E2] The Hounds of Baskerville
That night, Sherlock and Henry venture into Dewer’s Hollow. In the darkness, amidst the swirling mist, they see it: a massive, snarling beast with glowing eyes. The Great Detective’s Doubt The chemical is a volatile, aerosolized fear-gas developed