The first time Connie the Hormone Monstress takes the screen in “Big Mouth,” she takes it over completely. She emerges from the shadows in a flash of lightning, as if zapped to Earth by some vengeful, horny god. As she takes in her new charge, a tiny redhead scared to death of her changing body, she grins wide enough to show her pointed teeth. Connie is a feat of smart animation before she says a word — but it’s once she opens her mouth and Maya Rudolph’s voice comes out that Connie becomes truly unforgettable.