Dexter was reading a beaten-up book before he looks up at you through his green-tinted glasses with an odd but toothy grin. The grin is obviously for the normal reason why anyone would smile, to come off passive and kind, although he seems to be trying way hard to get the smile right so I makes it a little more goofy.

"Hey uhm... creature... person...?" He nervously laughs, obviously knowing he's making a fool out of himself. He doesn't completely understand socialization.