  Prominence bubbles are cavities rising into quiescent prominences from below.
The bubble-prominence interface is often the active location for the formation
of plumes, which flow turbulently into quiescent prominences. Not only the
origin of prominence bubbles is poorly understood, but most of their physical
characteristics are still largely unknown. Here, we investigate the dynamical
properties of a bubble, which is observed since its early emergence beneath the
spine of a quiescent prominence on 20 October 2017 in the H$\alpha$ line-center
and in $\pm$0.4 angstrom line-wing wavelengths by the 1-m New Vacuum Solar
Telescope. We report the prominence bubble to be exhibiting a disparate
morphology in the H$\alpha$ line-center compared to its line-wings' images,
indicating a complex pattern of mass motion along the line-of-sight. Combining
Doppler maps with flow maps in the plane of sky derived from a Nonlinear Affine
Velocity Estimator, we obtained a comprehensive picture of mass motions
revealing a counter-clockwise rotation inside the bubble; with blue-shifted
material flowing upward and red-shifted material flowing downward. This
sequence of mass motions is interpreted to be either outlining a kinked flux
rope configuration of the prominence bubble or providing observational evidence
of the internal kink instability in the prominence plasma.
