Just by looking at me?
Or can we be sure our assumptions about a person’s intentions are correct? Like Sherlock Holmes we have brains that get us from A to Z very quickly, and the journey via B, C D etc is often subconscious.
That’s fine if we are correct, but not so great if we confuse fact with assumption, or misinterpret things.
In the realm of human behaviour, people are notoriously difficult to interpret. I once reviewed two sets of minutes from the same meeting. Person A thought person B was calm. C thought B was very angry!
Sometimes we misinterpret people from our own misconceptions about them. Sometimes we hear what we expect to hear, not what was actually said.