Obligatory cat video:
LOL – I’d seen the cat filing claws gif before, but never the full video. Classic!
How about a prehensile rectum?
I could use another finger. When I mentally count on my fingers without looking at them, I will often assume that I have two of them instead of one in between my middle and pinky. So giving me another one would bring my body in line with my mind’s expectations.
I’ve already been warned about using my third thumb at work.
Spoiler- it’s not actually my thumb.
Prehensile Rectum. Still a classic.