Why Are Some People Double-Jointed?

http://www.thebeerbarrel.net/showthread.php?7794-Why-Are-Some-People-Double-Jointed

At any party, there's always that guy who can bend his fingers freakishly far back, and then brags about being "double-jointed" – but there's actually no such thing.

The term double-jointed implies that a person with unusual flexibility has twice the average number of joints, which allows for their increased range of motion. But that's anatomically impossible – except for rare instances, the majority of people have the same number of joints, the points in the body where two bones meet.