It has ties on the back that secure it in place.
There is a lot of complexity here, that needs appreciating. People will see you, and be like "Hey that's not a grandmother, that's a wolf! Now you, as a human, is going to dress up as a wolf.And if you see Little Red Riding Hood while you're out there, scare her for us, won't you? But not just any wolf, a wolf that is dressed up like a grandmother.