Researchers at the University of California have been working with a woman who was born with only three fingers on one hand.  At age 18, the hand was amputated following an accident, and she developed a phantom limb.  Most people have heard of phantom limbs, where amputated limbs can still be felt by their owners.

This woman’s phantom hand had all five fingers.

The researchers say this is a sign that the brain knows what the body should look like, even when it doesn’t actually look that way.

There’s a message here for anyone writing about shape-shifters.  From werewolves to alien possession, the brain would rebel against the new shape, and that should be either mentioned and explained as part of the story, or explained away with “magic”.

I’ve seen this done, actually – I read Stephanie Meyer’s “The Host” not so long ago, and when the alien bug takes over her new human host, there is a certain amount of disorientation which actually contributes to the plot.  It’s very well done.