We present high-resolution observations of two kinds of dynamic behavior in a quiescent prominence using the New Vacuum Solar Telescope, i.e., Kelvin-Helmholtz instabilities (KHIs) and small-scale oscillations. The KHIs were identified as rapidly developed vortex-like structures with counterclockwise/clockwise rotations in the Ha red-wing images at +0.3 angstrom, which were produced by the strong shear-flow motions on the surface/interface of prominence plumes. The KHI growth rates are estimated to be similar to 0.0135 +/- 0.0004 and similar to 0.0138 +/- 0.0004. Our observational results further suggest that the shear velocities (i.e., supersonic) of the mass flows are fast enough to produce the strong deformation of the boundary and overcome the restraining surface tension force. This flowdriven instability might play a significant role in the process of plasma transfer in solar prominences. The smallscale oscillations perpendicular to the prominence threads are observed in the Ha line-center images. The oscillatory periods changed nonmonotonically and showed two changing patterns, in which one first decreased slowly and then started to increase, while the other grew fast at the beginning and then started to decrease. Both of these thread oscillations with changing periods were observed to be unstable for an entire cycle, and they were local in nature. All our findings indicate that the small-scale thread oscillations could be magnetohydrodynamic waves in the solar corona.