Consequently, she was sitting in the staffroom making graphs with McGonagall's school census data, because she'd run out of student work to grade and all of her tests had been written years ago. McGonagall had only basic data, number of students in each House for every year and their gender and blood status, but from that she had been able to pull a remarkable amount of interesting information. Professor Snape, looking mildly amused, was sitting at the staff table drinking black tea, grading essays, and intermittently making sarcastic comments. (Septima Vector had been a Slytherin, and she and the Slytherin Head of House got along reasonably well.)