Although he was not invited to do so, Hannibal took a seat as the boy clearly didn't have a clue. The human's choice of leaning against the wall close to the door was an interesting one, it was unlikely a position chosen by his Master. Proximity to the door suggested a need to swiftly leave a room. Interesting.
"The study and treatment of mental illness, emotional disturbance, and abnormal behaviour" Dr Lecter informed the boy with a slight smile, wondering if that would serve as enough of an explanation of if he would have to dissect it further. It wasn't the boys fault of course, he was human and therefore had not received a proper education.