  Prominence bubbles, the dark arch-shaped "voids" below quiescent prominences,
are generally believed to be caused by the interaction between the prominences
and the slowly-emerging or quasi-stable underlying magnetic loops. However,
this scenario could not explain some short-lived bubbles with extremely dynamic
properties of evolution. Based on high-resolution H$\alpha$ observations, here
we propose that bubbles should be classified into two categories according to
their dynamic properties: quasi-steady (Type-I) bubbles and transient (Type-II)
bubbles. Type-I bubbles could remain relatively stable and last for several
hours, indicating the existence of a quasi-stable magnetic topology, while
Type-II bubbles grow and collapse quickly within one hour without stability
duration, which are usually associated with erupting mini-filaments. Analysis
of several typical Type-II bubbles from different views, especially including
an on-disk event, reveals that Type-II bubbles quickly appear and expand at a
velocity of $\thicksim$5--25 km s$^{-1}$ accompanied by an erupting
mini-filament below. The mini-filament's rising velocity is slightly larger
than that of the Type-II bubbles' boundary, which will lead to the collision
with each other in a short time, subsequent collapse of Type-II bubbles, and
formation of a large plume into the above prominence. We also speculate that
only if the angle between the axis of the erupting mini-filament and the
line-of-sight is large enough, the interaction between the erupting
mini-filament and the overlying prominence could trigger a Type-II bubble with
a typical arch-shaped but quickly-expanding bright boundary.
