The resolution is the part of the story that ties up the loose ends. In this case, it is when Sherlock explains to Dr. Watson how he solved the mystery. Sherlock Holmes had made the logical deduction that there must be a ventilator between Dr. Roylett's room and Julia's room because the sister had remarked that she could smell his cigar smoke. The house was undergoing renovation and the ventilator was made during this time. The bed was fastened to the floor so the person couldn't move it, and a cord was hung next to the bed. It was clearly not meant as a bell pull because nothing happened when it was pulled. Sherlock felt that something had to crawl down that bell pull. He knew the doctor had been getting creatures from India, and Sherlock figured that the doctor would be able to kill with a poison that was unknown in this fashion given his Eastern training. The creature was a swamp adder, a very poisonous snake. The whistle was the doctor's way of recalling the snake. He had trained it using the milk that was in his room. When the snake would return, he would then place the loop over the snake's neck and return it to the safe until the next night. Each night he would put the snake through the ventilator, knowing that it would crawl down the cord and land on the bed. Sooner or later it would bite the inhabitant of the bed. The metallic clang that Miss Stoner had heard was the doctor closing the safe. When Sherlock and Dr. Watson were in the room, Sherlock heard the snake hiss and attacked it with his cane. This action forced the snake back through the ventilator. It was angry and bit the first person it saw, which happened to be the doctor. The doctor died ten seconds later. Sherlock and Dr. Holmes found the snake curled around the doctor's head like a "speckled band". Sherlock Holmes is not sorry that he indirectly caused the death of Dr. Roylett.