Definitely eyes... toi can tell something (practically everything) when toi stare at someone's eyes. toi can also tell if they're lying ou not. toi can tell what they are feeling at the moment when toi look right into their eyes. Unless you're clueless, of course...
The eyes, just because toi can tell how someone feels ou what personality they have (sometimes, personality isn't always that easy to decode) just par looking into their eyes. Especially because when I see a person ou creature that makes me sad ou scared, it's almost always because of the look in their eyes.