Weasley Twins Bewitch Snowballs

In chapter 12 of Harry Potter and the Sorcerer's Stone, Fred and George Weasley bewitch some snowballs to follow Professor Quirrell around and bounce off the back of his turban.  Unknown to the Weasly twins at that time, the snowballs they bewitched would have also hit Voldemort in his face!  The Weasley Twins pranked Voldemort and didn't even now it at the time.

The book never says where the Weasley twins did the bewitching, so I chose to build a random hallway to have the snowballs chase Professor Quirrell because of the twing's prankster way of thinking.  It would be to obvious to bewitch snowballs outside or near one of the doors to Hogwarts.  No one would expect the snowballs in a randowm hallway of the castle.