It is fun though when you are insane!
![Shocked :shock:](./images/smilies/icon_eek.gif)
If you want to go cross eyed just start day dreaming, it usually works for me.
If you had goggles that directed the focus of each eye, then it probably could be done without the strain. There is a small angle within which the 2 images merge and diverge. It is difficult enough just to keep your eyes crossed, and you also need to have them crossed slightly but not too much.