unmoving pattern
A repeating clothing pattern (such as a checkerboard, plaid, or floral print) that does not follow the folds or contours of the clothes or body at all.
If there is no repeating pattern, use double exposure.
Featured in many, many anime, as it's much cheaper and easier than adjusting the pattern realistically. Particularly noticeable in stylized or minimalistic shows such as Sayonara Zetsubou Sensei and Bakemonogatari.