Selkie mermaid/human anatomy.

So a lot of times, I get kids who say, "But I saw you put your tail on!" or "I want to see you grow legs!"

This is how it works. Selkie anatomy is a LOT like human anatomy.

The diagram on the left is a selkie with her tailskin on. The right is a selkie, tail off.

The next diagram highlights the differences between the two skeletons. You'll notice that they are few, but distinct.

When a selkie mermaid transforms, it hurts, and this is why:

During the transformation process, The cartilage between the knee-caps, ankles, and feet, as well as the stuff that attaches the extra toes, breaks and separates. It then solidifies and becomes part of the tail skin. 

Most on land selkies have a bit of a high blood pressure for a while, since the heart is used to pumping blood through the additional appendages. 

When the tail skin is slipped back on, and water touches it, a chemical reaction causes the cartilage to reform and the extra toes to reattach themselves. Blood flow then eventually returns to normal, but only after some time swimming to get the heart rate up.

And there it is. The science of Selkie Mermaids.

Happy Tails!