its because how the screen works. if you looked at it from the side close up itd look like this
[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\[COLOR="red"]/[/COLOR]\
basically its displaying 2 pictures of the same thing, just with a slightly different angle. divides both into strips and the red would show 1 picture, and the black would show another. your left would focus on the red and the right eye on the black. when you take a screenshot, it doesnt really care if the screen is zigzaging, itll just pop a picture of every pixel being displayed. so itd be like taking the above diagram and just laying it flat, so youre seeing like alternating strips of 2 different pics being combined.
but most people know that already
Double post. Weird error. 
haha.
