Conjoined twins with partially fused brains:

Adding to the conundrum, of course, are their linked brains, and the mysterious hints of what passes between them. The family regularly sees evidence of it. The way their heads are joined, they have markedly different fields of view.

One child will look at a toy or a cup. The other can reach across and grab it, even though her own eyes couldn't possibly see its location. "They share thoughts, too," says Louise. "Nobody will be saying anything," adds Simms, "and Tati will just pipe up and say, 'Stop that!' And she'll smack her sister."

While their verbal development is delayed, it continues to get better. Their sentences are two or three words at most so far, and their enunciation is at first difficult to understand. Both the family, and researchers, anxiously await the children's explanation for what they are experiencing.

(Via Kottke.)