> > As I sit here, looking aimlessly into space, I think to myself... why do mirrors only reflect in the horizontal plane? Why not the vertical plane as well?
> >
> > Hmmm...
> >
> > Chr"No doubt the answer is obvious, but ah well..."ico
>
> Essentially it's because when we turn to look behind us, we're rotating our perspective about the vertical axis. Rotating half-way about the vertical axis flips the horizontal orientation of two objects but preserves the vertical orientation.
>
> Looking into a mirror is seeing this rotated perspective without actually rotating our heads.
>
> As a side note, note that beyond being a parallel line to the mirror plane, the preferred axis here is dependent upon the observer, not the mirror itself.
>
> --gremlinn


Yeah, grem explained it much better than I did. I thought about mentioning the 180 degrees rotation thing, but that was after I posted.