Limor Shifman Hamutal Ma'apil Varsano The clean, the dirty and the ugly: A critical analysis of 'clean joke' Web Sites. 2007 12 First Monday 2 http://www.uic.edu/htbin/cgiwrap/bin/ojs/index.php/fm/article/view/1621 db/journals/firstmonday/firstmonday12.html#ShifmanV07