4x15 - 3rd Rock from the Sun

Dick begins to feel that the unit is falling apart when Sally announces her plans to move out, and he tries in vain to clip her wings. That isn't the last of his problems, however, since Harry is considering having a baby with Vicki - despite the possibility that it could turn out to be an alien. Meanwhile, Tommy sees babysitting with Alissa as an opportunity to prove to a dubious Harry that she really is his girlfriend.