The supernova explosion of massive stars is primarily powered by the gravitational contraction of their core into a neutron star, before the formation of a black hole. Despite numerous observations of supernovae in distant galaxies, the underlying mechanism is still a major challenge to theorists. Prof Foglizzo will review the state of the art, with an emphasis on the multidimensional effects of hydro and MHD instabilities. Non axisymmetric one-armed instabilities known as the Standing Accretion Shock Instability and the corotation instability are able to redistribute angular momentum radially even for moderate rotation rates. Numerical simulations of simplified models are used to evaluate their effect on the explosion and the pulsar spin. Surprisingly, both instabilities can be illustrated with a simple hydraulic experiment based on a shallow water analogy. Results are analyzed in view of the constraints on the angular momentum budget set by stellar evolution on the one hand and by the spin properties of pulsars on the other hand.