 In a parody of the horror stories The Hunchback of Notre @-@ Dame ( 1831 ) and Basket Case ( 1982 ) , Bart and Lisa begin to hear strange noises , and think there is something in the attic . Homer claims not to know what they are talking about , although he is later seen grabbing a bucket of fish heads and heading into the attic . Bart and Lisa investigate , and discover there really is a monster . Homer and Marge go into the attic , and Homer says : " Oh no , it escaped " . Marge immediately calls Dr. Hibbert , who explains that Bart had a conjoined twin brother named Hugo . The two were separated at birth , but it was discovered that Hugo was too evil to live in society , so the Simpsons did the " only humane thing to do " : they kept Hugo chained in the attic , where Homer fed him a platter of fish heads once a week . The rest of the family leaves to find Hugo , leaving Bart behind , but he soon discovers that Hugo never left the house . Hugo takes Bart up to the attic and ties Bart up , so that he can reattach himself . Suddenly , Dr. Hibbert finds them and knocks out Hugo , commenting that the evil twin is always on the left side . But then he realizes that Hugo 's scar is on the wrong side , and Bart is the evil twin . In a failed attempt to correct their wrong , Dr. Hibbert and the Simpson family sit down to a turkey dinner with Hugo , leaving Bart locked up in the attic eating fish heads . 
