The symbol of many autism awareness groups is a multicolored puzzle with a piece missing. I'm sure you've seen car magnets like that a lot more often than you used to, automotive symbols of how fast autism has exploded and how many people are dealing with it, so you know what I'm talking about. There are several reasons for the symbol, from 'solving the puzzle of autism' to 'every person with autism is different' to 'the mystery of what causes it'. It may have as many meanings as autism has different effects.
But I see another facet.
Xander likes some things in their wholeness - give him a Bear in the Big Blue House show, or Zoboomafoo, and he'll watch it from beginning to end. (I use 'watch' loosely, since jumping up and down and running back and forth is his usual TV viewing positions. He may be the rare person who loses weight when the TV's on.) But others? He'll only watch parts of them. He has clear favorites - opening themes and closing credits of most shows, but the middle he doesn't care about. I've noticed if given his choice on music, he will do the same - not just particular songs on a CD, but only up to a certain part of it, then he asks for another song, which will again go to a part and then stop. Books as well - certain parts he loves and will open to that point time and again. Rest of it? Take it or leave it.
(I once saw a list of 'things you never knew until your kid had autism' and one of them was how much fun credits are, so his love of them doesn't seem unique. It may just be the up and down scrolling on the screen that so interesting; Xan also loves to watch me play Guitar Hero. As to why it's so doggone funny, who knows? Because it's different, vertical moving inside of horizontal fixed?)
Speaking outside my experience, this seems to fit in other autistic conditions. For example, many Asperger's people tend to fixate on one particular thing, like trains or art or dinosaurs, and learn about it everything they can. And as I said in another posting, the single-minded focus on one thing - one piece, if you will - on the playground or in the classroom is quite common.
Maybe this love of certain pieces of a whole fits in with the sensory issues - certain parts sound, or look, better. Like us having a favorite part of a book or movie or song, but in his case it's not just liking it more, but having it fit in more, make more sense, feel better. As evidence of this, the parts Xander does like, he can take loud. When it's a scene he likes - the final space and land battle in Serenity, or the Green Dragon fight in How To Train Your Dragon - no matter how loud it gets, all-the-way-up-things-vibrating-off-the-shelves-loud, he'll jump and laugh and run back and forth and stay in the room to watch it. Other parts, he covers his ears and leaves.
I wish I could say there was something in common with what he likes, but none that I can tell. High-pitched lasers; deep explosions; plinkly banjo music; a crunchy guitar chorus; 'they must not get our apples down/come on come on get out of town!' (Ten Apples Up On Top by Dr. Seuss, for those of you past the Dr. Seuss stage); an end page picture of...well, nothing really. Random pieces here and there of sounds and sight that fit into his senses better than the rest of the world.
A fitting puzzle piece that's a puzzle in itself.