In both cases 4) and 5) you might say something was hidden. But note the different application of “hidden”.
6).   Compare with this: You read a letter and can't read one of its words. You guess what it must be from the context, and now can read it. You recognize this scratch as an e, the second as an a, the third as a t. This is different from the case where the word “eat” was covered by a blotch of ink, and you only guessed that the word “eat” must have been in this place.
7).   Compare: You see a word and can't read it. Someone alters it slightly by adding a dash, lengthening a stroke, or suchlike. Now you can read it. Compare this alteration with the turning in 5), and note that there is a sense in which while the word was turned round you saw that it was not altered. I.e., there is a case in which you say, “I looked at the word while it was turned, and I know that it is the same now as it was when I didn't recognize it”.
8).   Suppose the game between A and B just consisted in this, that B should say whether he knows the object or not but does not say what it is. Suppose he was shewn an ordinary pencil, after having been shewn a hygrometer which he had never seen before. On being shewn the hygrometer he said that he was not familiar with it, on being shewn the pencil, that he knew it. What happened when he recognized it? Must he have told himself, though he didn't tell A, that what he saw was a pencil? Why should we assume this?