Sibling Rivalry?

Ok, so yesterday Elora was being especially uh... what's the right word... contentious? with Max. She kept taking toys away from him and throwing them across the room, pushing him down, and one more thing... When Max was asleep upstairs, Elora and I was downstairs. Elora heard Max wake up, and said, "Max awake!" So she goes upstairs to greet him I thought... I was doing something downstairs, so it was a few minutes before I went upstairs to get Max. Well, before I went up there, I hear Max crying hysterically. So I went upstairs and find Max crying in his crib buried under all of the kid's books! Elora had taken ALL of the children's books that we have on the shelf in our bedroom and she put them all in the crib on top of Max. So I unbury Max, pick him up and console him... I just don't understand what possessed Elora to do this... It is really unbelievable... But I guess that's a two year old for you!