A harmless case of URL manipulation.
Go to a page on the web that contains a lot of images like a Google image search or something. (Note: this won't work on this site becasue it uses frames)
Once the page has loaded, delete the address from the address bar and replace it with;
javascript:R=0; x1=.1; y1=.05; x2=.25; y2=.24; x3=1.6; y3=.24; x4=300; y4=200; x5=300; y5=200; DI=document.images; DIL=DI.length; function A(){for(i=0; i
Edit, this forum puts a space between java and script that shouldn't appear in the URL, take that out.
hit 'go' and watch the show.