  We compute the dynamics and emission of dissipative shells that are subject
to a strong Compton drag, under simplifying assumptions about the dissipation
mechanism. We show that under conditions prevailing in blazars, substantial
deceleration is anticipated on sub-parsec and parsec scales in cases of rapid
dissipation. Such episodes may be the origin of some of the flaring activity
occasionally observed in gamma ray blazars. The shape of the light curves
thereby produced reflects the geometry of the emitting surface if the
deceleration is very rapid, or the dynamics of the shell if the deceleration is
delayed, or initially more gradual, owing, e.g., to continuous injection of
energy and momentum.
