You can also cup your hand on a flat surface and hit it with the bottom of your other hand and the same thing will happen
Certain areas of skin have more nerve endings than others. Basically this is a protection mechanism.....areas, such as fingertips, that are very prone to injury are very sensitive to pain (so that you automatically will pull away from the source of danger). Try this....pinch starting at your elbow and work your way down to your hands....you will notice the pain sensation is worse the closer you get to your hands. (Same thing with knees to toes). The skin on your elbow is less prone to do something such as touch a hot stove, so it is less necessary, plus, the skin on your elbows and knees is thicker and tougher than that on other parts of your body so it can take a bit more of a beating.
Impossible, I am super-sensitive... =.=
I still feel stuff.