  Fast microjets can emerge out of liquid pools from the rebounding of
drop-impact craters, or when a bubble bursts at it surface. The fastest jets
are the narrowest and are a source of aerosols both from the ocean and a glass
of champagne, of importance to climate and the olfactory senses. The most
singular jets, which have a maximum velocity of 137$\pm$4 m/s and diameter of
12 $\mu$m under reduced ambient pressure, are produced when a small dimple
forms at the crater bottom and rebounds without pinching off a small bubble.
The rebounding of this dimple is purely inertial but highly sensitive on
initial conditions. High-resolution numerical simulations reveal a new focusing
mechanism, which drives the fastest jet within a converging conical channel,
where an entrained air-sheet provides effective slip at the outer boundary of
the conically converging flow into the jet. This configuration bypasses any
viscous cut-off of the jetting speed and explains the extreme sensitivity
observed in detailed experiments of the phenomenon.
