  Analogue black holes, which can mimic the kinetic aspects of real black
holes, have been proposed for many years. The growth of the radial momentum of
test particles toward the acoustic horizon is calculated for acoustic black
holes in flat and curved spacetimes. Surprisingly, for a freely infalling
vortex approaching the acoustic black hole, the Lyapunov exponent of the growth
of the momentum at the horizon saturates the chaos bound $\Lambda_{\rm
Lyapunov}\leq 2 \pi T$. We investigate the orbits of test vortices and sound
wave rays in the $2+1$-dimensional "curved" spacetime of an acoustic black
hole. We show that the vortices orbit, the sound wave orbit, and the time delay
of sound are similar to those famous effects of general relativity. These
effects can be verified experimentally in future experiments.
