He argues that they should bear the higher freight charge of 30¢ for livestock, rather than the lower 25¢ for domestic pets.
Because the customer refuses to accept delivery, Flannery is forced to feed and house what he now calls the "dago pigs" in his office.
When he eventually receives instructions to accept the lower price, he discovers that the customer has moved.
The story was made into movie form several times, including the Walt Disney cartoon in 1954 that was nominated for an Academy Award for Animated Short Film.
The rapid reproduction of the guinea pigs and their near overrunning of a facility is mirrored by the Martian flat cats in the Robert A. Heinlein novel The Rolling Stones.