A pair of conjoined twins, sharing a direct neural connection. There is evidence that the girls can sense what the other twin is sensing:
This suggests two things:
* High bandwidth Brain-Computer Interfaces (BCI) ought to be possible (no surprise, but it's good to have strong evidence)
* The brain is a general purpose machine. It doesn't have specific modules for 'Left Hand', 'Right Hand', etc. Rather, it takes in information and makes sense out of it. It does this even when the setup is haphazard (as the connection between the twins' brains must be). On the other hand, we know the brain *does* have specific modules (such as the visual cortex among many others), which makes an interesting dichotomy.
I predict that the main hindrance to high functioning BCI is getting sufficient bandwidth, not figuring out how to decode/encode signals properly.