tl;dr:“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? Second, are they curious? Do they reciprocate by asking questions about you? Are they genuinely interested or just being polite? 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?”