Sitting on a braided rug was a boy of about nine deeply engaged with a tablet computer.

      “This is Mr. Sedgwick,” she said.

      The boy looked up from the floor and extended his hand. Travis bent down and had to hold the boy’s hand with his fingers, but managed a serviceable shake.

      “What are you doing?”

      “It’s a kind of illusion I found on YouTube.”

       Travis looked but saw only a red circle and some white dots.

      “What does it do?”

       “It explains everything.”