  When a liquid viscous bridge between two parallel substrates is stretched by
accelerating one substrate, its interface recedes in the radial direction. In
some cases the interface becomes unstable. Such instability leads to the
emergence of a network of fingers. In this study the mechanisms of the
fingering are studied experimentally and analysed theoretically. The
experimental setup allows a constant acceleration of the movable substrate with
up to 180 m/s$^2$. The phenomena are observed using two high-speed video
systems. The number of fingers is measured for different liquid viscosities and
liquid bridge sizes. A linear stability analysis of the bridge interface takes
into account the inertial, viscous and capillary effects in the liquid flow.
The theoretically predicted maximum number of fingers, corresponding to a mode
with the maximum amplitude, and a threshold for the onset of finger formation
are proposed. Both models agree well with the experimental data up to the onset
of emerging cavitation bubbles.
