The blush is charming, a marker of qualities like relative innocence, and Caleb's momentary hesitance is probably only visible to a person schooled in analyzing minute facial expression. Vincent is markedly appealing on a number of external and less tangible levels, and the fact that she lacks - let us just be blunt - what appears to be burgeoning psychosis isn't a drawback, as Caleb is not quite that off in his proclivities, but it is a factor he files away.
Of course, he doesn't per se frame it as 'damn, it's a shame she isn't obviously contemplating what all my possessions would look like if she took a baseball bat to them in six months,' but ...for a Divination major he has yet to really identify certain facets of that particular pattern. None of which means that he isn't enjoying the conversation, ergo the reticence of less than a second is gone before it can really even form, and his lovely smile is still easy. "Yeah? That'd be another first. Should I bring anything special? Hedgehog treats?"