I'm extremely flexible too.
I can put a foot behind my head and stand up on the other leg... but I have to use my hands to hold onto something while doing so, because I can't balance.
I can touch the back of my head with my toes. I don't know if you can visualize that, because I don't know how to explain it in words. Imagine what Katura is doing in her pictures, except rightside up. As in my hips are on the floor instead of my chest, and my toes touch the back of my head.
You know that yoga position where each foot is on top of the other leg? I can get into that position without using my hands to put my legs there. If I'm on a trampoline, I can jump into the air and land like that.
I can lick my elbow. You've probably been told it's impossible... well, whoever told you that is wrong, because I can do it.
However, despite being able to do those things, I can NOT touch my toes without bending my knees.
I can also make interesting sounds with my voice. I can meow like a cat very convincingly, like enough to fool people into thinking there's a cat in the room. I can make REALLY high-pitched sounds with my voice. High-pitched sounds don't hurt my ears, and that's probably why... because I can make them myself.
Oh, and I can do that thing with my fingers where the joint closest to the tip is bent and the other joint is perfectly straight. I don't think that's very uncommon, because I've met a lot of people who can do it, but there are also a lot of people who can't.