  Two- and three-dimensional simulations demonstrate that hydrodynamic
instabilities can lead to low-mode (l=1,2) asymmetries of the fluid flow in the
neutrino-heated layer behind the supernova shock. This provides a natural
explanation for aspherical mass ejection and for pulsar recoil velocities even
in excess of 1000 km/s. We propose that the bimodality of the pulsar velocity
distribution might be a consequence of a dominant l=1 mode in case of the fast
component, while higher-mode anisotropy characterizes the postshock flow and SN
ejecta during the birth of the slow neutron stars. We argue that the observed
large asymmetries of supernovae and the measured high velocities of young
pulsars therefore do not imply rapid rotation of the iron core of the
progenitor star, nor do they require strong magnetic fields to play a crucial
role in the explosion. Anisotropic neutrino emission from accretion contributes
to the neutron star acceleration on a minor level, and pulsar kicks do not make
a good case for non-standard neutrino physics in the nascent neutron star.
