Pigs is Pigs
Based on a short story of the same name by Ellis Parker Butler that was first published in 1905.
Flannery is a station master who does everything by the book. One day, a package of guinea pigs arrives at his station. Flannery assumes by their name that they are pigs but one customer, McMorehouse, who wishes to purchase refuses to pay 48 cents for pigs because he thinks they are pets and should be 44 cents. Flannery decides to write to the head office and asks if they are pigs or pets. While waiting for an answer, the pigs begin to multiply. After a few days, the station is literally filled with guinea pigs and Flannery finally realizes they are pets, not pigs. He goes to McMorehouse’s home to deliver them but McMorehouse has moved. Flannery decides to send all the guinea pigs to the head office and learns his lesson about handling pets. Says Flannery, “If the animals come in singles or if they come in sets, if they’ve got four feet and they’re alive, they’ll be classified as pets!”
Plot summary: IMDb