The most important symbol in the book is certainly the outrageous premise, which paints life as a Mexican or Mexican American through the metaphor of robotics. By making Mexicans into robots, the novelist turns a question back on the reader. Do people pigeon-hole others based on racial prejudice and assumption? The novelist shows the dehumanizing effects of treating people as perfectly predictable, and in the end, Mrs. Jiminez is in for a harsh wake up call.
In the end, the climactic revelation is that, surprise, the Mexicans were always people the whole time. They weren't really robots at all. Also, they begin revolting, crying "Viva la revolucion," which is an indication that they feel they are mistreated lower class folks. The mistreatment is obvious, and so is the patronizing relationship between Mrs. Jiminez and the Mexicans.
For instance, she is literally trying to buy a Mexican. Now, because they're robots, that means it isn't slavery, but the ending of the novel reveals that they were humans. Their mistreatment is clear, and other common prejudices about Mexicans and Mexican Americans are addressed by the plot, and then dismissed. The real people are a sign to Mrs. Jiminez that her money can't protect her as well as she thought, and when she leaves, she leaves behind the money she would have used to buy a slave, and the Mexican "robot" people get paid for their mistreatment.
