@CLamb is right it has to be very low resistance otherwise it doesn’t create a strong magnetic field because the electrons can’t move enough. A wet arm wouldn’t really do anything either, even if it did create the opposing magnetic field it would be applied to the water not your arm which would just sort of shift on your skin. Same basic idea with a screw in your arm, only the screw would feel the force so it might move or push on the bone it was screwed into.
