Claire Perry knows a split second can change everything. It can be the difference between sticking a perfect landing or falling off the beam. It can be the difference between a really fun party or a totally messed up one. Or sometimes, as Claire finds out, it can even be the difference between life . . . or death. For Claire's younger sister, Nellie, an elite gymnast who is "destined for gold," things have always come easy. A split second is usually...