The corridor outside the library intersects (On Thursdays) with another corridore that happens to lie on the most direct route between the herbology greenhouses and the Slytherin common room.

And it just so happens that Melaka Fray, who has a habit of making bets with the seventh years about what she can or can't steal from the Professors, has just had a narrow escape in the Herbology greenhouses and wants to put as big a distance between them and herself as quickly as possible.

Usually she has pretty good spatial awarenesws. Today she is sprinting all out down that corridor.

Naturally, the resultig collision is spectacular.