Bart gets injured while doing a stunt on the roof of his house. He goes to the hospital and Dr. Hibbert cuts his hair to apply stitches to his head. It is soon revealed that Bart has a birthmark on his head that is similar to the one Ned Flanders has.
Todd has the same scar, but Rod does not leaving everyone to indicate that Bart and Rod were switched at birth. After confronting Ned about it, Ned admits he does have the birthmark on his arm. Soon Bart is living with Ned and Todd, while Rod is living with The Simpsons.
Bart and Rod needless to say have a tough time adapting to living with different families. After Bart has taken a bath, Ned comes in and washes behind his ears.
After completing the task, Ned discovers that Bart's birthmark is in fact dried up bubblegum that was on his head. After Bart and Rod return to their original families things go back to normal. Bart insults Homer, who in turn strangles Bart once again. Marge is glad to have Bart home while Lisa misses Rod.