The rectal exam is a delicate art to learn. Doctors perform this procedure entirely by feel, with just one finger. Students who are learning how to do such an exam have no way of showing their work to their teachers. And volunteer subjects are—unsurprisingly—rare. In the entire United Kingdom there’s only one person registered as a test subject for rectal exams, says Fernando Bello, who works on surgical computing and simulations at Imperial College London.