Question: why are some people double jointed ?

Reka Nagy answered on 10 Nov 2016:

It all depends on the way bones come together and move – as you may know, joints are the areas where two bones meet. Bones themselves are quite rigid, and joints allow them to move. People who are double-jointed have greater flexibility in their joints so their bones can move a lot more with respect to each other.

We believe that the shallower the shape of a joint is, the bones that are part of this joint are able to move more.

This is not always a great thing, as people who are double jointed find that it is easier for them to dislocate a joint, which can be quite painful to fix!