Proximity

After the park, Sam brought Cassandra and her new dog to Dr. Fraiser's. Janet explained to Cassie that dogs required lots of exercise and sent them outside to get some.

When the door closed, Janet asked Sam the eternal question, "How did you know?"

"I was going up the elevator, getting farther and farther away from her, thinking about how she was alone when all she'd wanted was for me to be near her, and how horrible it was to turn a little girl into a bomb. Suddenly I knew that the naqahdah in her bloodstream was a proximity fuze."