If it starts to puss up there is something in there. You body will try and eject anything, usually by forming a big puss pocket and that moves to the surface until you squeeze it or scratch enough until it pops out with the foreign body. When the nail comes back be sure and coach it along so it doesn't grow under the skin. Such a simple thing that can turn into a giant pain in the azz(finger). Also, if it gets red and swollen with streaks running out of it go to the doctor. Might be a serious infection. Pretty rare but you could lose the finger or hand if it gets really infected.
