A general term for accidental or deliberate changes that scribes made while copying texts. They may be errors of omission, of addition, of transposition or of alteration. Errors of omission include two types of eyeskip: homeoteleuton, when the scribe paused, then resumed copying from a later section because of the similarity of the endings of two lines; and homeoarchy, when the scribe skipped a passage because of the similarity of the the beginning of two lines. Haplography is when the scribe copied once a word or syllables that appear twice in the older text. Errors of addition include dittography (repetition of words or letters) and contamination (extraneous element from elsewhere is copied on the page). Metathesis is an error of transposition, in which words, letters, or phrases are reversed. Alterations can be accidental or deliberate, especially when the scribe attempted to improve the original.