Seems like it should be 3 1/2 inches, doesn’t it? But if you think about where page 1 of Volume I is when the books are lined up the usual way (Volume I on the left), you’ll see that the worm actually passes through only one volume’s worth of pages. It seems like, since you transferred pure wine to the water and only a mixture back, there must be more wine in the water than water in the wine. But that can’t be right, because then you would have increased the total amount of wine! No matter what you do, if you end with a liter of liquid in each carafe, there must be the same amount of wine in the water carafe as there is water in the wine carafe. The flaw in the first argument is that although you transferred less than a spoonful of water to the wine carafe, you returned some of the wine.