Such were the little visual games that MAD would play back in it's heyday, and this one was a real whopper! /laughs
Well, if I knew that in that distant past of seeing this cover, I had forgotten it!
You are right. There is IS something there that doesn't belong - ha-ha - an extra finger...or the artist was not good at drawing hands! :)
Just the ‘Mad’(madcap) brand of humor, I think!
J.