Visit http://think101.org to learn more about this illusion and how our experience affects what we see.
This is a new scientific finding called the "Flashed Face Distortion Effect". You can read more about it here: http://mbthompson.com/research
Tangen, J. M., Murphy, S. C., & Thompson, M. B. (2011). Flashed face distortion effect: Grotesque faces from relative spaces. Perception, 40, 628-630 doi:10.1068/p6968