I think theres a time for jokes, and a time for not... but i think smiling and laughing is a good thing.. .... I've had them give the poker face look too, but usually I dont say or mention that I see through it, unless there IS a connection...
But sometimes just sitting back and talking and having a okay time for a session is nice... especially if it's the only place that you feel safe and don't really want to bring the hell from outside within the safe place..