Gareth, apparently spotting some opportunity to show off, demonstrates precisely how un-wobbly his finger is. Strange boy.

OK, try this at home: spread your fingers out like this (remember, if any of these pictures is too small to see clearly, just click it for a larger view).

Now, bend just one of your fingers at the knuckle, like this.

Flick that finger with your other hand, and you should find it wobbling around like nobody’s business. It doesn’t hurt – but you don’t seem to have any control over it, either.

Not that Fred ever has much control, but he finds the same thing. See if you do, too.

What’s going on? Well, there are two tendons that run up your forearm. They then branch out to your fingers.

One tendon branches to your middle knuckle, the other to your fingertips.

But here’s the thing; you don’t have perfect control over your fingers. The tendons stretching to your fingertips only work if your middle knuckle tendons are activated.

Sounds weird? Not at all. Try to bend just the last joint of your fingers. If you can do this at all, you’ll only be able to move your fingertips a tiny amount.

But, if you make a claw, like this, the middle tendons are activated, and you’ll be able to bend all your fingertips through ninety degrees.

In the claw, you’ll find that all your fingers are rigid – none are doing the wobbly thing we started with.

But if you now straighten up three of your fingers, you’ll feel a moment when the middle tendons release, and the curled finger goes all floppy. Go on, try it!