Tell us the narrowest special interest you have had in life, I mean super narrow, not necessarily intense, just really specific, if a usual special interest for an autistic is a book, then an unusually narrow one is a book's specific page.
two come to mind for me right now:
*The 18th second of radioheads song "videotape" http://www.youtube.com/watch?v=Qvv-LpTBWVk
*A musical chord I don't know the name of, but I just came across it accidentally. If you have a piano: go to the A minor triad below middle C, which is ACE, and bring the A note down a half step to G#, so it's G#CE unbroken triad.
I've constructed a whole peice around this single chord that I've just played over and over as the bass chord for various peices - right now it goes ACD, G#CD, GCD (which is C major) pulsating unbroken triads repeated quietly but quickly, I adore it.
Can anyone beat me with something even more narrow? 
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'not only has he hacked his intellect away from his feelings, but he has smashed his feelings and his capacity for judgment into smithereens'.