Metaphors may help understand the process of deduction

Watson gamely struggles with various metaphors to describe the process of deduction, so that the unfamiliar can be illuminated by analogy with the familiar.

Deduction is the unravelling of a tangled ball of twine.

There's plenty of thread, no doubt, but I can't get the end of it into my hand [TWIS].
--- to devise some common thread upon which they might all hang [MUSG].
--- you broke the thread of my thoughts. --- I have now in my hands all the threads which have formed such a tangle [STUD].
Different threads, but leading up to the same tangle [RUDC].
There is a thread here which we have not yet grasped and which might lead us through the tangle [DEVI].
It is a tangled skein, you understand, and I am looking for a loose end [CREE].
There's the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it [STUD].
Deduction is the forging of a chain of links.
It is so long a chain, and yet every link rings true [REDL].
The last link. My case is complete [STUD].
I only require a few missing links to have an entirely connected case [SIGN].
It's the chain between them that we are going to trace [VALL].
It was by concealing such links in the chain that Watson was enabled to produce his meretricious finales [BLAN].
When you follow two chains of thought, Watson, you shall find a point of intersection which will approximate the truth [LADY].
Deduction is the playing of a game of cards.
We are getting some cards in our hand. --- it is not an easy one to play [SHOS].
We have added one card to our hand [SHOS].
Alas that I should have to show my hand so when I tell my own story [BLAN].
Each metaphor, I must confess, he took from my own mouth - or, in some cases, put into my mouth. The thread metaphor is so mixed that it, in itself, is a tangled ball. I further confess that the metaphors got mixed, with two or more metaphors within a single case - indeed, even within a single paragraph. Metaphors are helpful aids to make concrete what is basically an abstract process. However, now that I have the leisure to contemplate my career, I believe that the most useful metaphor for what I was doing is that I was telling a story. Since this metaphor applies not so much to deduction per se but to the entire process of detection, I will explore it at more length in Chapter 8 - Explanation.