The jet is launched into the stellar envelope following the collapse of the stellar core. The jet propagation inflates a hot pressurized bubble, known as "the cocoon". Due to the lateral motion of the relativistically heavy jet into the lighter cocoon in the first collimation shock. Then the jet becomes instable to Rayleigh-Taylor instabilities (RTI) that form on the plane perpendicular to the jet's axis. As soon as the first collimation shock is closed, forms a new shock that expands radially, inducing Richtmeyer-Meshkov instabilities that develop on the same plane with the previous RTI. This behavior repeats, albeit at a smaller extent, at the second collimation shock.