Why does he look at me every time he enters the room?

We're in the same major so we share a few classes, though we've never really spoken one on one before. I've only caught him looking at me a handful of times otherwise, but he does laugh at like everything I say. I looked at him yesterday as I was smiling and then he started smiling too... does he seem interested or am I just desperate?
Why does he look at me every time he enters the room?
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