"All Singing, All Dancing" is the eleventh episode of Season 9 (originally going to be the last episode of said season, but "Natural Born Kissers" took it's place).
Anticipating a bloody Clint Eastwood-Lee Marvin shoot-'em-up, Bart and Homer are horrified to discover that their video rental, Paint Your Wagon, is actually a musical. Several song and dance moments from seasons past are recalled.
Homer rents the movie Paint Your Wagon for the family to watch. He and Bart expect to see a violent Western movie starring Lee Marvin, Clint Eastwood and someone who appears to be Lee Van Cleef. However, the truth is that the movie is actually a musical. This causes Homer to dispose the tape and condemn singing, but Marge says that Homer often sings.
After that, Bart sings an insult about Homer's singing, which leads Homer to strangle Bart when Marge sings that Bart had also sung "and danced like a girl". This leads to when Bart sang Springfield, Springfield with Milhouse in Boy-Scoutz 'n the Hood. When this flashback is done, Snake Jailbird jumps into the house through an open window and warns the family not to move or he shall blow their heads off.
After those flashbacks, Snake suddenly returns through the window, singing that he got annoyed with their music from his first visit and plans to kill them all for getting a song stuck in his head. Homer then says that he should have closed the window.
Homer sings of being convinced, but when Snake hops through the window once again and starts singing that he is finally going to kill them, Marge says that they are finished singing. Snake then told her that he had no reason to kill them, so he leaves once again. The Simpson family then prepare for dinner while Marge closes the window and hums. Snake, who just heard Marge's humming, fires a bullet at the window, making the glass break, which Marge says "Okay! Okay! Sorry!" During the end credits, Snake is heard shooting the theme song, making it stop for a few seconds, then play very quietly afterwards. Snake still hears it, and shoots at it again. Finally, when the Gracie Films logo is seen, he even shoots the music there and says, "You, too, Gracie music dude! Gaw!"