This is not only the nature of the body but also the nature of the mind; the mind cannot think of two things at the same time. Also, when the mind is at work and fully absorbed in a certain thought, a certain imagination, the outer senses may be open, but they are not fully at work. When a poet is thinking of a verse, the verse is before his mind. His eyes are open, but he does not see; and if it happens that he sees anything when he is thinking, then it is just like a moving picture. So many different pictures coming one after the other that they seem to be continuous. When the mind stops, the eyes work, and when the eyes work the mind stops; and in the end it seems to make one picture, but in reality it is a separate action of the mind and of the senses. It is also true that the wakeful state of every individual is different and peculiar to himself, just as the sleep of every individual is different and peculiar to himself. One person will be what is called fast asleep, that is to say in deep sleep. Another will be half asleep. Another knows what is going on around him, and yet he is asleep. This shows that the extent of sleep is different in every experience, and no one can classify this extent of sleep.