Dr. Mortimer, suddenly skeptical, questions Holmes' guess work, and the Holmes retorts that his methodology involves weighing probabilities and deciding on the likeliest solution. To prove it, he points out that the spluttered writing suggests a lack of ink, undoubtedly the result of a hotel pen, and not a private one. Holmes even asserts that an investigation of hotel garbage around Charing Cross, where the letter was postmarked, should yield the torn-up copy of the Times.