Brennan can understand that. She's not sure she can explain it very well, but she can understand it.

"It's only when something or someone means a great deal to us that it hurts when it's lost."

She makes an attempt at a smile.

"At the genetic level we're social creatures. We require emotional attachments, even though logic tells us that those attachments will all inevitably end someday, one way or another. But we form them anyway. It's one of the things that makes us human."