In Chapter Four, Sir Henry Baskerville tells Sherlock Holmes of his surprise when he received a letter upon his arrival at the Northumberland Hotel. According to Sir Henry, no one but Dr. Mortimer had been privy to his plans. What surprises Sir Henry even more is the content of the letter.
The letter contains only one line which reads "As you value your life or your reason, keep away from the moor." What is even more surprising is that all the words, except one, have been cut out from a newspaper. The only word that has been written in ink is "moor." Sherlock Holmes deduces that the author of the letter had likely cut out the words from the Times newspaper, as he recognizes the distinctive print on the paper.
Holmes also surmises that the author is someone who is educated and also someone who wishes to remain anonymous, hence the pasted words on the letter. As it is very often possible to determine the likely identity of a letter-writer from the handwriting, the writer appears to have used the pasted words to evade detection.
Another puzzle that concerns Sir Henry is that, after he put a pair of boots outside his hotel room to be cleaned, only one has been returned to him. Although a singularly perplexing incident, Holmes thinks that the boot will turn up eventually. To Holmes, the most important consideration is whether it is safe for Sir Henry to go to Baskerville Hall. He warns Sir Henry that he will likely face danger if he decides to go there. However, Sir Henry is adamant that he will go, maintaining that he will not intimidated to stay away from the home of his own family.