A multifrequency analysis of the short-term photometric variations of the Be and shell star EW Lac is performed. Two data sets, almost thirty years apart, revealed similar frequency structures but significantly differ in amplitudes. The causes of variability is checked under various assumptions including spot(s) on the surface, an inhomogeneous or asymmetric envelope, tidal distortions, and the presence of a companion. The most plausible interpretation is, however, found in terms of nonradial pulsations. In particular, the problem of abrupt light changes is pointed out, an effect which is fully explained by multiperiodicity.