  The 2001 outburst of WZ Sagittae has shown the most compelling evidence yet
for an enhancement of the mass transfer rate from the donor star during a dwarf
nova outburst in the form of hot-spot brightening. I show that even in this
extreme case, the brightening can be attributed to tidal heating near the
interaction point of an accretion stream with the expanding edge of an
eccentric accretion disc, with no need at all for an increase in the mass
transfer rate. Furthermore, I confirm previous suggestions that an increase in
mass transfer rate through the stream damps any eccentricity in an accretion
disc and suppresses the appearance of superhumps, in contradiction to
observations. Tidal heating is expected to be most significant in systems with
small mass ratios. It follows that systems like WZ Sagittae - which has a tiny
mass ratio - are those most likely to show a brightening in the hot-spot
region.
