  We present an analytic study of the mode-coupling phenomena for a scalar
field propagating on a rotating Kerr background. Physically, this phenomena is
caused by the dragging of reference frames, due to the black-hole (or star's)
rotation. We find that different modes become mixed during the evolution and
the asymptotic late-time tails are dominated by a mode which, in general, has
an angular distribution different from the original one. We show that a
rotating Kerr black hole becomes `bald' slower than a spherically-symmetric
Schwarzschild black hole.
