"I had a hypothesis that the one-time pads were being drawn up by a person who was rolling dice or shuffling a deck of cards to produce the letters. I began to consider psychological factors. An English speaker is accustomed to a certain frequency distribution of letters. He expects to see a great many e’s, t’s, and a’s, and not so many z’s and q’s and x’s. So if such a person were using some supposedly random algorithm to generate the letters, he would be subconsciously irritated every time a z or an x came up, and, conversely, soothed by the appearance of e or t. Over time, this might skew the frequency distribution."