But if I had to write down what it is that makes someone seem smart, I’d emphasize three things. First, do they know stuff? Ask them what they’ve been thinking about and probe them about it. Do they seem to understand it in detail? Can they explain it clearly? (Clear explanations are a sign of genuine understanding.) Do they know stuff about the subject that you don’t?
Second, are they curious? Do they reciprocate by asking questions about you? Are they genuinely interested or just being polite? Do they ask follow-up questions about what you’re saying? Do their questions make you think?
Third, do they learn? At some point in the conversation, you’ll probably be explaining something to them. Do they actually understand it or do they just nod and smile? There are people who know stuff about some small area but aren’t curious about others. And there are people who are curious but don’t learn, they ask lots of questions but don’t really listen. You want someone who does all three.