To truly appreciate the latest Simpsons couch gag you need to see The Simpsons: The Longest Daycare, a 4½ minute short shown before Ice Age: Continental Drift (embedded below). In the short, Maggie is sent to a dystopian daycare. There she encounters her arch-nemesis Gerald Samson AKA Unibrow Baby, who squashes all but one butterfly that Maggie manages to save. This time she saves them all.
