What sort of variation with time could cause a QPO? For example, the power spectrum of an oscillating shot appears as a continuum of noise together with a QPO. An oscillating shot is a sinusoidal variation that starts suddenly and decays exponentially. A scenario in which oscillating shots cause the observed QPOs could involve "blobs" of gas in orbit around a rotating, weakly magnetized neutron star. Each time a blob comes near a magnetic pole, more gas accretes and the X-rays increase. At the same time, the blob's mass decreases so that the oscillation decays.