Randy is looking at Kepler pretty carefully when he says this, and there’s no doubt that genuine astonishment is now spreading across the Dentist’s face. The Dentist only has one facial expression (already described) but it changes in intensity; it gets more so and less so depending on his emotions. The Dentist’s expression proves he had no idea, until now, that Randy’s been allowed to have a computer in his cell. In the trying-to-figure-out-what-the-fuck-is-going-on department, the computer is the single most important datum, and Kepler didn’t even know about it until just now. So to whatever extent the Dentist actually gives a shit, he has a lot of thinking to do. He excuses himself pretty soon after.