I consider it an actual phenomenon, but I'm not sure it's a phenomenon of somebody's eyes (facial expressions, technically speaking) or of my own perception.
Essentially, it's a snap judgement of whether a person is bright or dull and, in my experience, it works out quite well.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.