文档介绍：Holmes had been seated for some hours in silence with his long, thin back curved over a chemical vessel in which he was brewing a particularly malodorous product. His head was sunk upon his breast, and he looked from my point of view like a strange, lank bird, with dull gray plumage and a black top-knot.
     "So, Watson," said he, suddenly, "you do not propose to invest in South African securities?"
     I gave a start of astonishment. Accustomed as I was to Holmes's curious faculties, this sudden intrusion into my most intimate thoughts was utterly inexplicable.
     "How on earth do you know that?" I asked.
     He wheeled round upon his stool, with a steaming test-tube in his hand, and a gleam of amusement in his deep-set eyes.
     "Now, Watson, confess yourself utterly taken aback," said he.
     "I am."
     "I ought to make you sign a paper to that effect."
     "Why?"
     "Because in five minutes you will say that it is all so absurdly simple."
     "I am sure that I shall say nothing of the kind."
     "You see, my dear Watson" -- he propped his test-tube in the rack, and began to lecture with the air of a professor addressing his class --"it is not really difficult to construct a series of inferences, each dependent upon its predecessor and each simple in itself. If, after doing so, one simply knocks out all the central inferences and presents one's audience with the starting-point and the conclusion, one may produce a startling, though possibly a meretricious, effect. Now, it was not really difficult, by an inspection of the groove between your left forefinger and thumb, to feel sure that you did NOT propose to invest your small capital in the gold fields."
     "I see no connection."
     "Very likely not; but I can quickly show you a close connection. Here are the missing links of the very simple chain: 1. You had chalk between your left finger and thumb when you returned from the club last night. 2. You put chalk there when