From a NYT article about conjoined twins

The average person tends to fall back on the Enlightenment notion of the self — one mind, with privacy of thought and sensory experience — as a key characteristic of identity. That very impermeability is part of what makes the concept of the mind so challenging to researchers studying how it works, the neuroscientist and philosopher Antonio Damasio says in his book, “Self Comes to Mind.” “The fact that no one sees the minds of others, conscious or not, is especially mysterious,” he writes. We may be capable of guessing what others think, “but we cannot observe their minds, and only we ourselves can observe ours, from the inside, and through a rather narrow window.”

This is the article. Makes one think about individuality. And the mind.