Cori Schmidt, 12, went through a life change Tuesday, moving from the giggling-at-everything stage of adolescence to the never-smiling stage. 'My goodness, just the other day, I accidentally left a pair of old pantyhose on the couch, and she was jumping all over the living room giggling hysterically,' Hannah Schmidt, 41, said of her maturing daughter. 'But now, everything I say to her is met with a gloomy scowl.' Asked if she was aware of her passage into sullenhood, the younger Schmidt said, 'I don't know,' without making eye contact. 