Charles looks at a bottle of French perfume that Mr. Oleson presents to him, for his buying consideration. Michael Landon reads its name as: "Fragrance de Amor". "Amor" is a Spanish word, and the French word "de" is abbreviated to remove the vowel. Therefore he should have read in French, "Fragrance d'amour". Later, Caroline Ingalls reads this, in proper French. ("Da-moor" is how it is pronounced in French, not "de-a-more", as Landon erroneously did.)
Molly the B and B owner uses the phrase "Let's trip the light fantastic". This phrase was not used until 1894 in the song "Sidewalks of New York" by Charles B. Lawlor and James W. Blake. Molly uses it roughly 12 years before it was written.