Snowballs can be bewitched to fly around and hit things.
Fred and George bewitched snowballs to hit Quirrell's turban, unwittingly hitting Voldemort in the face. They received detention for it (PS12).
While the fifth years were busy studying, other kids bewitched snowballs to fly up and hit the windows of the Gryffindor common room to tease them (OP21).
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