  We present optical integral field spectroscopy (IFS) observations of the
Mice, a major merger between two massive (>10^11Msol) gas-rich spirals NGC4676A
and B, observed between first passage and final coalescence. The spectra
provide stellar and gas kinematics, ionised gas properties and stellar
population diagnostics, over the full optical extent of both galaxies. The Mice
provide a perfect case study highlighting the importance of IFS data for
improving our understanding of local galaxies. The impact of first passage on
the kinematics of the stars and gas has been significant, with strong bars
likely induced in both galaxies. The barred spiral NGC4676B exhibits a strong
twist in both its stellar and ionised gas disk. On the other hand, the impact
of the merger on the stellar populations has been minimal thus far: star
formation induced by the recent close passage has not contributed significantly
to the global star formation rate or stellar mass of the galaxies. Both
galaxies show bicones of high ionisation gas extending along their minor axes.
In NGC4676A the high gas velocity dispersion and Seyfert-like line ratios at
large scaleheight indicate a powerful outflow. Fast shocks extend to ~6.6kpc
above the disk plane. The measured ram pressure and mass outflow rate
(~8-20Msol/yr) are similar to superwinds from local ULIRGs, although NGC4676A
has only a moderate infrared luminosity of 3x10^10Lsol. Energy beyond that
provided by the mechanical energy of the starburst appears to be required to
drive the outflow. We compare the observations to mock kinematic and stellar
population maps from a merger simulation. The models show little enhancement in
star formation during and following first passage, in agreement with the
observations. We highlight areas where IFS data could help further constrain
the models.
