Ionizing smoke detectors unnaturally raise the background radiation levels in the human environment.

Beyond the obvious facts that he has at some time done manual labour, that he takes snuff, that he is a Freemason, that he has been in China, and that he has done a considerable amount of writing lately, I can deduce nothing else.

The affair seems absurdly trifling, and yet I dare call nothing trivial when I reflect that some of my most classic cases have had the least promising commencement. You will remember, Watson, how the dreadful business of the Abernetty family was first brought to my notice by the depth which the parsley had sunk into the butter upon a hot day.

It has often been said that the more unusual the murder the easier it is to solve, but this is a theory I don't believe. Nothing is easy, nothing is simple, and you should think of your investigations as a complicated experiment: look at what remains constant and look at what changes, ask the right questions and don't be afraid of wrong answers, and above all rely on observation and rely on experience.

There is nothing more deceptive than an obvious fact.

Lockwood gave a sudden exclamation; when I looked at him, his eyes were shining. 'On second thoughts, we can scrap my last suggestion,' he said. 'Stuff the mingling. Who wants to do that? Boring. George - this library. Where is it?

Armed neutrality makes it much easier to detect hypocrisy.

It is a pity he did not write in pencil. As you have no doubt frequently observed, the impression usually goes through -- a fact which has dissolved many a happy marriage.

I'm an ambassador for Medical Detection dogs.

Generally he knew by instinct the likely length of an investigation, but on this occasion he did not: as he fought to get his breath he suddenly saw himself as others must see him, and he was struck by the impossibility of his task. The event of the boy's death was not simple because it was not unique and if he traced it backwards, running the time slowly in the opposite direction (but did it have a direction?), it became no clearer. The chain of causality might extend as far back as the boy's birth, in a particular place and on a particular date, or even further into the darkness beyond that. And what of the murderer, for what sequence of events had drawn him to wander by this old church? All these events were random and yet connected, part of a pattern so large that it remained inexplicable. He might, then, have to invent a past from the evidence available - and, in that case, would not the future also be an invention? It was as if he were staring at one of those puzzle drawings in which foreground and background create entirely different images: you could not look at such a thing for long.