  Prominences are incredibly dynamic across the whole range of their observable
spatial scales, with observations revealing gravity-driven fluid instabilities,
waves, and turbulence. With all these complex motions, it would be expected
that instabilities driven by shear in the internal fluid motions would develop.
However, evidence of these have been lacking. Here we present the discovery in
a prominence, using observations from the Interface Region Imaging Spectrograph
(IRIS), of a shear flow instability, the Kelvin-Helmholtz sinusoidal-mode of a
fluid channel, driven by flows in the prominence body. This finding presents a
new mechanism through which we can create turbulent motions from the flows
observed in quiescent prominences. The observation of this instability in a
prominence highlights their great value as a laboratory for understanding the
complex interplay between magnetic fields and fluid flows that play a crucial
role in a vast range of astrophysical systems.
