If you open and close scissors the main force is up/down but based on the structure of the hand you also apply a sideways force which twists the blades left/rig

If you open and close scissors the main force is up/down but based on the structure of the hand you also apply a sideways force which twists the blades left/right. Depending if the top blade (where your thumb goes in) this pushes the blades closer together, or a bit apart. And if the hinge has to much play, this is enough that the paper gets twisted between the scissors.