“Leela’s Homeworld” (Season 4, Episode 2)

For the first three seasons of the show, it was assumed that one-eyed space captain Leela was an alien from a now-probably extinct race. However, in this episode, it’s revealed that she’s a mutant and her parents lied about her origins so she could live on the surface while they lived in the sewers. (This plot point was first hinted at in a random crowd shot in Season 2 because the writers of this show were wild.) What really makes this episode stand out is the end, where we see how her parents secretly cared for her. Is that dust in my eyes?