"One morning Mr Sherlock Holmes was sitting in his room in Baker Street. His friend Dr Watson, was standing near the window looking at a walking stick.This stick had been forgotten by a strange visitor the day before. The words "To Dr Mortimer" was written on it. Dr Watson had already been examining it for half an hour but he couldn't say anything about it. Suddenly Sherlock Holmes said: The owner of this stick has a dog which is larger than a terrier. I have noticed the marks of a dog's teeth on the stick.' Probably the dog often carrys the stick behind the master,' he added. 'I wonder why this man wanted to visit us,' asked Dr Watson. 'Well, we shall soon know,' answered Sherlock Holmes. 'I can hear the bell ringing.' "