Sherlock Holmes is at Helen Stoner's house, looking for the cause of her sister's death.
We inspected the window. No one could pass these shutters once they were bolted.
Yes, and we bolted them every night!
They realize that whatever caused the death had to come from inside the bedroom, because the windows and door were locked.
It doesn't ring? How absurd! I never noticed that before!
Why, this bell is a dummy! It doesn't work!
Watson and Sherlock wait till night, when they here a whistle coming through the bell.
Sherlock strikes at something with his cane and lights a match. They hear a scream. Holmes tells Watson it was the speckled band, a deadly snake from India.