  Shear-thinning fluids exhibit surprisingly rich behaviour. One example is the
Kaye effect which occurs when a thin stream of a solution of polyisobutylene in
Decalin is poured into a dish of the fluid. As pouring proceeds, a small stream
of liquid occasionally leaps upward from the heap. This surprising effect,
which lasts only a second or so, is named after its first observer A. Kaye, who
could offer no explanation for this behaviour. Later, Collyer and Fischer
suggested from 250 frames per second cine recordings that the fluid must be
highly shear thinning as well as elastic and 'pituitous'. In addition, they
concluded that a rigid surface is required to back the reflected liquid stream.
While the words bouncing and reflection are associated with non-continuous and
elastic effects, we will show here that the Kaye effect is in fact a continuous
flow phenomenon. We show that the Kaye effect works for many common fluids,
including shampoos and liquid soaps. We reveal its physical mechanism
(formation, stability and disruption) through high-speed imaging. The
measurements are interpreted with a simple theoretical model including only the
shear thinning behaviour of the liquid; elastic properties of the liquid play
no role. We show that the Kaye effect can be stable and that it can be
directed. We even demonstrate a stable Kaye effect on a thin soap film
excluding the necessity of a rigid backing surface.
