Bruce didn't bother taking attendance because he made it clear during his first class that if students didn't show up, they wouldn't pass the exams that made up 60% of their grade. He wasn't the kind of professor who taught straight out of the textbook or based his exams solely on the readings. He took great effort in making his lectures engaging, interesting, and educational and expected his students to attend and take notes.
That being said, he did pay attention and knew every student in the class by sight, if not by name, and it didn't escape his notice when a young redhead started slipping in to attend his lectures. She didn't disturb the class, so he didn't object to her presence, but the more she showed up, the more curious he became. It was easy enough to flirt a bit with one of the women in the registrar's office and find out who she was.
Today, after wrapping his lecture, he immediately headed out of the lecture hall, following the young woman to the coffee stand at the nearby student center. He stood in line behind her and, when the barista said her total, pulled out his credit card. "I've got it," he said.