Making new friends helped her 'come out of her shell'. = Making new friends 'brought her out of her shell'.
He lost confidence in himself and 'retreated/withdrew into his shell'.
The police found several spent 'shells' at the scene of the shooting.
(..) Some people aren't. We know that about you now, okay? What do you think I am? Pearls. Galen finds 'em in the mussel shells. Come on, let's get that book. - You weren't havin' any fun? - No! - No fun at all? - No! (..)2012 Mud