Both my thumbs are double-jointed. I can make the joint pop out to a really disgusting degree at will.
I can dislocate my shoulders and put them back at will, without touching them.
I can bend my pinky backwards and touch the back of my wrist with it.
I can do the Vulcan-live-long-and-prosper thing, but only with my right hand.
I can flare my nostrils to an astonishing degree.
I can fold my tongue backwards, so the tip points down my throat and hold it in that position for a ten count.
I can crack every joint in my body. Fingers? Pfft. Try toes/ankles/knees/hips/back… guess the hockey has had an effect on me. Nothing feels better than twisting just the right way and feeling all your vertebra pop in sequence. 
:: pops her back. ahhhhhhhhhhhh ::
The index finger on my right hand was broken playing volleyball such that it doesn’t bend in the middle. I never had it set and now can point around corners.
I can wiggle my eyes at will. They shake very fast. It creeps kids out.
I, too, can turn my left eye in while keeping my right eye facing forward.
It’s a gift.
I can fold my left pinkie up into my left fist and close my fist around it, so it looks like I am holding on to some random finger. I do this and show it to kids and say “hey, look what I found!” Yux all around.
Nostril flaring, knuckle cracking (by no means limited to knuckles - the whole bone repetoire), and full-on ear-wiggling, meaning when I wiggle my ears, it looks like I am moving my entire scalp back and forth, kinda like a toupee.
I’ve got that “one-eye-inward” thing, too… but, now that I notice it, it actually goes OUT. Amblyopia sucks. I didn’t even get a cool eyepatch when I was a kid- I just got a bandage, which made it look like I’d manage to gouge my eye out, or something. Now I just ignore everything that eye sees.
I used to be able to blow bubbles, underwater, out of the corner of my left eye… allergies don’t allow that anymore, though on bad allergy days the corner of my eye squeaks.
I can wiggle my ears and raise an eyebrow. I can also wiggle my scalp.
The weirdest thing, though, is that I can bend my arms really far backwards at the elbow. It looks like I’ve broken my arms.
Not much to see here…
I can curl my tongue. But just into a circle. And only the once.
I can raise my arch my right eyebrow Mr. Spck style. The left one doesn’t work like that though.
I can move one eye at a time, but this is just a trick. (Look to the left, cross my eyes, look to the right and back again.)
I can put my palms together and squeeze out air making a “fart” sound. Kids love this.
Uhhh… that’s about it.
-Rue.
I can make squirrel barking noises…good enough to get them down for a close look.
I can recognise people I know by sense of smell. Ditto recognise their clothing.
I can smell rain coming.
I have an educated sniffer.
I can keep one eye looking straight forward, and move the other around. It really creeps a few people out.
I can talk in a “satan-voice” that sounds really creepy.
I can pop one of my thumbs out of joint and back again at will.
I don’t really know how to describe it, but I can open my throat, which makes the underside of my chin/top of my neck expand, so I resemble a bullfrog.
I can do the OP’s eye thing with either eye. It’s fun to do when having a serious discussion with someone, makes them lose their train of thought.
For a heated argument, or just to get someone’s goat, which I really don’t need any more of, I’ve got a whole bunch by this time, you should smell my living room, it really tends to freak out the opposition.
The above sentence makes sense… read it again.