The implosion that disconnects a submerged air bubble
into several bubbles provides a simple example of energy focusing.
The most efficient disconnection is an entirely cylindrically-symmetric one
terminating in a finite-time singularity. At the final moment,
the potential energy at the start of the disconnection is
entirely condensed into the kinetic energy of a vanishingly small
amount of liquid rushing inwards to disconnect the bubble. In
reality, however, the initial shape always possesses slight
imperfections. We show via theory, numerics and experiments
that a detailed memory of the imperfection remains and often
controls the final fate of the focusing.