RYu finished his lunch in blissful silence, and with quite a bit of time in the lunch period to spare. So he took his time returning to the classroom, silently observing fellow students as he passed. A girl in the hall was obviously incredibly vain, given the sheer amount of cosmetics and the perpetual hand mirror that seemed all but glued to her hand. He passed a boy who's dark circles under his eyes indicated he was either something of an insomniac or he played a lot video games in poorly lit rooms. 

And this went on until he reached his classroom where Ryu took his seat, the earlier phenomena returning to the forefront of his thoughts. What could cause four people to hallucinate simultaneously? It might be worth some minor of investigation and to that end Ryu pulled a medical encyclopedia from his bag, quickly scanning the index for what he was looking for. Yes, just a bit of light reading until afternoon classes started.