  Light curves of superhumps and their evolution during superoutbursts are
analyzed by decomposing them into their Fourier components, including the
fundamental mode and the first three overtones. The amplitudes of the
fundamental mode are found to decrease significantly during superoutburst while
those of the overtones remain practically constant. The phases of maxima of the
fundamental mode {\it increase} systematically during superoutburst while those
of the overtones -- systematically {\it decrease}. The combination of the two
effects is responsible for the characteristic evolution of superhump light
curves: the appearance and growth of the secondary humps and the spurious phase
jumps in the (O-C) diagrams. Two intrepretations are possible. Either that
instead of just one superhump period $P_{sh}$ there are four periods $P_k$
which resemble -- but are significantly different from -- the fundamental mode
and the first three overtones of $P_{sh}$. Or -- more likely -- that those
time-dependent phase shifts are genuine.
