Deborah Tannen, university professor of linguistics, on the bond between sisters:

"It's the double meaning of the word bond. There's the bond of a connection and the bond of bondage ... When you are connected to somebody, everything each one does affects the other, and it's a kind of bondage. You're not as free as you would be if that person wasn't in your life."

Sisters Speak In 'You Were Always Mom's Favorite'

September 8, 2009, NPR