When Phil Hartman died suddenly and tragically, the producers of The Simpsons decided not to recast his characters but to simply retire them.
This particular episode is the last appearance of Troy McClure, hosting another science video and ending it with a cheesy, embarrassed grin. That may be the best way to send the character off, all things being equal.
After Bart and Lisa were offered a place in “Who’s Who In American Elementary School Students” book, Marge treats the family to a day out at the family fun park where there are go-carts and batting cages to injure Homer and an arcade where Nelson can jimmy open a ski ball machine to get enough tickets to get himself a BB-gun. Bart, impressed, asks to use it some time. Nelson is amenable, but Marge sure isn’t. Marge believes Nelson is a troubled, lonely boy, and as such he should be avoided as much as possible.
But Bart disobeys and goes anyway to the old shack Nelson calls home. Nelson dares Bart to shoot a bird in her nest, and while Bart deliberately aims away, the crooked sight means Bart manages to kill the bird anyway. Marge finds out where Bart went and orders the boy home, which Nelson joyfully originally thinks means him, but then Marge finds out Bart killed a defenseless bird. Bart, wracked with guilt, asks to be punished, but Marge doesn’t see the point anymore. Maybe all those stray cats nosing around the dead bird were the give-away.
But then Bart learns there were eggs in the nest and takes it home to take care of. Killing the mother bird was bad enough, but he doesn’t want to be responsible for the eggs too. A film tells him a lightbulb can incubate the eggs, and after borrowing one from the Simpson house, we get multiple moments of Homer falling down the basement stairs since there’s no longer a light there.
But using Marge’s good gray extension cord makes Marge suspicious and Bart’s care means Marge finds her heart opening up and soon the whole family is working to hatch the eggs, a moment Homer finds more exciting than when he saw Hailey’s Comet collide with the moon. Too bad that never happened.
And then the eggs hatch! And good for Bart, he’s a mother to a pair of lizards.
Well, it turns out the eggs were a pair of Bolivian tree lizards, as revealed by Principal Skinner in his role as the leader of the Springfield Birdwatching Society. And the lizards are dangerous to local birds because they tend to eat birds and drive them to extinction. The lizards have to die, but Bart doesn’t want them to, and while Marge covers for her son and his hatchlings, Bart allows the lizards to glide to safety. Soon they’re overwhelming the city and…everybody loves them.
See, the lizards are basically wiping out the local pigeon population. And there are plans to bring in other invasive species to gradually wipe out each previous invasive species. Winter will finish off the gorillas and cause the end of the whole thing. Bart gets an award in the form of a scented candle.
So, he felt bad for killing one bird directly, but then he was fine about his actions inadvertently killing many, many birds.
Such is life.