you dont need to be on shrooms to halucinate. i just tried this and holy shit it is theeeee trippiest thing i have ever seen. stare at the middle of it and the nlook away. the results will be incredible! make sure to look at the screen the whole time though. there is no popup and scare the shit out of you type thing either
http://www.break.com/index/cool_optical_illusion.html