Taboos
What is not talked about
Every culture draws a circle around certain topics, and the location of that circle is one of the first things worth mapping when you arrive somewhere new.
Taboos are not arbitrary. They protect what a culture considers sacred, dangerous, or simply too charged for casual handling: death and dying, bodily functions, sex and reproduction, money and debt, certain foods, politics, religion, mental illness, disability, and dozens of other territories depending on context. Some taboos are explicit (there are laws or rituals around them), but many operate as unspoken mutual agreements: everyone knows not to go there, even though no one said so.
The difficulty with taboos is that they are often invisible until you cross one. The silence itself can be the only signal, and by then the discomfort is already in the room. Moving between cultures means learning to read that silence, to notice the sudden shift in atmosphere, the change of subject, the flicker of discomfort on someone's face. It also means being willing to sit with uncertainty: you may never fully know which topics are off-limits and which are simply not coming up by chance.