  In interacting and merging galaxies, gas is subject to direct hydrodynamic
effects as well as tidal forces. One consequence of interactions is the rapid
inflows of gas which may fuel starbursts and AGN. But gas dynamics is not
limited to inflows; a small survey of equal-mass and unequal-mass encounters
produces a wide variety of features, including plumes between galaxies,
extended disks formed by infall of tidal debris, and counterrotating nuclear
disks. An even richer spectrum of behavior awaits better thermodynamic models
for gas in merging galaxies.
