While the audience is used to hearing Stewie (voice of Seth MacFarlane) speaking in erudite Ivy League tones, in the world of the show's characters, he's still a baby who can't be understood by his grown-up human family members. In the season premiere, "Stewie's First Word" – also the show's milestone 350th episode – the little boy hits that developmental milestone, but his first word of choice is filthy. Shunned by other moms, Lois (voice of Alex Borstein) tries to figure out where Stewie picked up that obscenity.