I had a go at making a Stereoscopic animation. To suit the Virtual Boy 3D aspect, so the Left image represents the left lens and the right image represents the right lens. The game is Aliens 3D. A 3D FPS.
All you need to do is cross your eyes so that the two pictures meet in the middle. It may take a bit of practice to get it, but I assure you it works. (not as good as some other examlpes on the internets)
If you can't get it to work by crossing your eyes, just keep trying and eventually you'll get a headache making it even more like the Virtual Boy experience :)