The Atoner: Nels seeks to make amends with his estranged sister, but can't bring himself to approach her due to feeling ashamed of how he treated her in the past.
Comedic Underwear Exposure: When Laura, participating in the circus show as a clown pulls Christy Norton's dress, which she hadn't properly sewn, it falls apart exposing her petticoat. It's played for laughs because Christy is a snob and unpleasant to everyone (though Laura did that because she was a rival to Almanzo).
Foreshadowing: Look closely when Harriet and Willie Oleson are mocking Annabelle (Nels' previously unknown sister) at the circus: Nellie does not take part. You'll recall that she wholeheartedly took part in the festivities earlier, but once her father reveals that the circus woman is his sister, she no longer does so and becomes very quiet. And at the climax, when honorary ringmaster Nels proudly reveals to the audience (basically all of Walnut Grove) that the "fat lady" is his estranged but beloved sister, Nellie (unlike her mother and brother) puts on a positively glowing smile and rises to her feet, applauding. These are early seeds of the Heel–Face Turn Nellie Oleson undergoes in the next season.
Only One Name: Circus ringmaster London is known only by said moniker, even claiming at the beginning to have no last name.
You Look Familiar: Guest star Billy Barty (Owen) would later play the titular character in season 9's "Little Lou" (who is also a circus performer, albeit one who has just left said profession after the birth of his daughter).
You Look Familiar: Guest star Billy Barty (Owen) would later play the titular character in season 9's "Little Lou" (who is also a circus performer, albeit one who has just left said profession after the birth of his daughter).