S21E14 Postcards from the Wedge
Bart is slacking again. Homer feels he should have more home-work but Marge takes a kindlier approach. Bart succeeds in playing them off against each other until they tumble to the fact and kiss and make up. Seeking a truly awesome prank Bart and Milhouse activate the old Springfield subway system,setting off an earthquake. But who is behind the anonymous note informing Homer of Bart's next big stunt?