Meanwhile, outside the greenroom, the three alien high schoolers are gathered around a set made to look like a clearing in the forest, examining a mysterious symbol in the grass. This symbol, which has a clear connection to the aliens who crashed – and, presumably, to the one other alien who’s still alive – is a central motif in the kids’ quest to learn about their extraterrestrial background.

It’s also the kind of thing that can lead to a little tomfoolery. As they crouch in the clearing, Behr, Heigl and Fehr can be seen in the background of the shot be cannot be heard; the real action is taking place in the foreground, between the sheriff and his son. As they lengthy scene plays out, the two boys decide that the strange symbol – a dot surrounded by curving lines – resembles a breast. Under the guise of examining it, they begin to caress it lewdly. Heigl keeps a straight face until the scene ends, and then she erupts as the guys laugh. “You idiot!” she yells, whacking Fehr on the back with her flashlight. That was so bad. You idiot!”

Watching the good – nature melee, Behr thinks back to other on-set jokes, and shrugs. When the scenes are very intense, we don’t lose our focus,” he says. “But when the scenes are lighter, we all laugh till our sides hurt. And don’t let them fool you – the girls can get as crass and as base as the guys.”

After she stops pounding on Fehr, Heigl laughs off the typical high school – style hijinks – because, after all, what is Roswell but a show about typical high-school kids who turn out to be not so typical? “At this age, everybody is trying to figure out who they’re from,” she says. “The only difference is, we’re also trying to figure out what planet we’re from.