There is something wrong with the original. There is a passage in "The Signs of Four" in which Watson sat down and began to massage his legs because of Holmes' attitude. His leg was injured in the war in Afghanistan. After treatment, it has not hindered walking, but once the weather changes, this injured leg also hurts like hell. "Signs of Four" also said that Watson needed crutches when he went out, and he limped when he pulled the dog to chase the murderer.