At nine months old, Autumn started banging her head. Victoria and Nathaniel had installed swings for their twin girls in the doorway of the living room, and Autumn would lean out of the swing in order to whack herself on the posts. They would carefully snuggle her back in, secure her, and pad the posts with pillows, but she continued to bang. Sometimes she banged with such vigor that she scarred herself and shook the house. She also started to rock, vigorously pulsating back and forth. She...