In addition to the other comment detailing where Cirno was, Rumia is also slightly visible (It's a second or two before the part where Reimu's at the fridge)
Obviously none of you saw the genius of Cirno. She allowed herself to get knifed because she would be the one to get the fewest injuries that way. If she falls first then Sakuya will be spending so much time chasing the others that Cirno can escape with just a mere flesh wound. (Nods)
