Which statistical features distinguish a meaningful text (possibly written in an unknown system) from a meaningless set of symbols? Here we answer this question by comparing features of the first half of a text to its second half. This comparison can uncover hidden effects, because the halves have the same values of many parameters (style, genre, etc). We found that the first half has more different words and more rare words than the second half. Also, words in the first half are distributed less homogeneously over the text. These differences hold for the significant majority of several hundre...