Have you ever wondered just what makes up a turtle shell? I know when I was a kid, I thought it grew right out of its back and around its body, because the turtle shell that my dad found in the woods and gave to me still had a backbone in it, attached.

 It turns out that I was pretty close.

Japanese scientists at the RIKEN Center for Developmental Biology in Kobe, Japan have discovered that turtle shells are actually made from their own shoulder blades and rib bones. According to the study, published in Science journal, while in the egg, the shell completes a strange but cool folding process that pushes the turtle’s shoulder blades straight into its own ribcage, which makes the ribs grow around them, creating the shell.

Is that not the weirdest thing you’ve heard all day? Raphael and Michelangelo may have thought they were freaks because of the mutant goo in their blood, but I think if they knew that their bodies sort of grew inside out while in utero, they’d still need therapy.

In the study, the scientists took a look at the Chinese soft-shelled turtle as well as a chicken and a mouse, watching how the embryos developed. In the turtle, a “disk-shaped thickening of the skin on the back” occurred, which didn’t happen with the other species. This caused the ribs to grow outward but still into the disk, which creates the shell’s shape.

The big discovery here is that the shell is actually part of the turtle, not just an accessory—or the turtle’s “home,” as we always called it. So think about that next time you want to paint your name in nail polish on the next turtle you come across.

That always pissed me off when I was a kid when other kids did it—didn’t they know that would be a glaring sign for predators? “Duh, this way I’ll be able to know he’s ‘mine’ if we meet again.” No, Moe, it means you’ll never see him again because he will be breakfast, idiot.

But now that we know it’s actually a part of the reptile’s actually body, it’s not as random, right? Would you spray paint your name on, say, the white strip of a skunk? Well, probably not, but still—the shell isn’t a fun rock to play with, it’s a turtle-part.

“In cartoons, you sometimes see a turtle take off its shell like a coat. A turtle cannot do this. It is not simply a shelled reptile. It has modified its basic body plan a great deal,” reminds study coauthor Shigeru Kuratani.