Complex sentence: As Sherlock and John prepare to leave the next morning, John wonders why he saw the hound in the lab despite not having inhaled the gas from the hollow, but later realises Sherlock locked him in the labs in order to test his theory.
Split into simpler sentences: As Sherlock and John prepare to leave the next morning, John wonders why he saw the hound in the lab despite not having inhaled the gas from the hollow. He realizes that he was poisoned by leaking pipes in the laboratory earlier.He later realises Sherlock locked him in the labs in order to test his theory.