Have you ever heard of such a thing?
I sure hadn’t.
But when I saw the howto wiki link on my igoogle this morning I was curious enough to click it.
Apparently shadow knitting / illusion knitting is a form of knitting where you knit in a hidden image which is only visible from a certain angle. That’s… kinda awesome!
I really am considering trying this out. Of course I’d have to learn how to knit first and judging by my track record of not having the patience to learn anything new this might not ever happen even though I’m excited about it now but eh, we’ll see
Here’s the link to the wiki thing and here is another one with a bunch of patterns and example photo’s so you can see how cool it is for yourself. I really love the Pirate skull and crossbones one.
I’d also love to have a Slytherin scarf done in this method, just to wear it out and scare the crap out of small children 
But yeah basically if you’re creative you can do any pattern you want really.
-Dee.
[EDIT]
I just messed around a bit and made my own pattern for a Slytherin scarf

Ok I’m getting excited now lol.
This would be the hidden image on a normally white and green striped scarf. (The black being the places where the white wool would be. Though I’m kinda leaning towards making it black and green because I like that combo better even though it’s not the original Slytherin color combo)
This is a really cropped version by the way just so it’ll fit in my blog.
If anyone’s interested in this pattern let me know and I’ll send you the full size one (in which the stitch squares don’t look that messy, meh at resizing and what it does to lines).
[/EDIT]