I'd like to point out that the queen metroid, with her whole huge mouthful of very sharp teeth was unable to harm Samus in any way while she was screw attacking. It also renders more interesting attacks such as the baby metroids' suck-the-life-force-out-of-anything-that-moves-that-isn't-a-metroid attack useless; never mind that Samus is completely encapsulated by the baby metroid.