It is a prolapse.
http://www.dendroboard.com/forum/general-health-disease-treatment/7859-bubble-coming-out-butt.html
http://www.dendroboard.com/forum/general-health-disease-treatment/5035-help-rectal-prolapse.html
and you may want to read http://www.dendroboard.com/forum/care-sheets/16433-emergency-supportive-care.html
http://www.dendroboard.com/forum/general-health-disease-treatment/7859-bubble-coming-out-butt.html
http://www.dendroboard.com/forum/general-health-disease-treatment/5035-help-rectal-prolapse.html
and you may want to read http://www.dendroboard.com/forum/care-sheets/16433-emergency-supportive-care.html