Bifid Thumb
This is not incredibly rare, it does occur from time to time, actually, 1 out of every 1000 people have what is known as a bifid thumb. The medical term for it is preaxial polydactyly and basically what happens is that a person’s thumb branches out into two parts as shown in the picture.
So it does not mean that you have 6 figures on one hand instead of 5, it just means that one finger is doubled. It can look a bit strange at first but after staring at it we can not help but think about all the strength they must have in that thumb.