Replying to Cold Hands

I don't know how many people know this trick, but i figured it out this past weekend. If you straighten your arm as much as you can and bend your hand pointing outward...and drop your shoulder repeatedly, you will warm your hands within 10 seconds and never have cold hands again. It should hurt a bit and you can feel the blood shooting into your arm. Again, a bunch of people probably know this already, but for those of you who don't...youre welcome. I may have saved you from some cold hand days.