In "Those Who Don't," Sanda Cisneros writes, "Those who don't know any better come into our neighborhood scared. They think we're dangerous. They think we will attack them with shiny knives." She says that they're stupid and got lost and are there by mistake. She goes on to explain that when she's in a neighborhood and everyone there is brown like her, she's safe. When she is familiar with a place, she can relax and feel at home. Lack of familiarity breeds fear.
It isn't that the people in her neighborhood are dangerous. It's that the visitors don't know any better and are scared of what might happen.
To make it clear that it's not something that affects one group of people, she says, "But watch us drive into a neighborhood of another color and our knees go shakity-shake and our car windows get rolled up tight and our eyes look straight." This shows how nervous they are. They are so scared that their bodies are reacting by shaking and they're looking around, alert and aware that there could be potential trouble.
The speaker knows that racial prejudice happens because of a lack of understanding. People are familiar with what they know; in this case, that's represented by their racially distinct neighborhoods. Once they venture outside those boundaries, they're outside their comfort zone. They react with fear because all they know are the views of the people there that they've heard from others. Prejudice guides their feelings and actions.