We performed simulations of a bubble rising in a viscoelastic medium. Clicking on the picture will show you an animation.
It is easier to see the change in the shape of the bubble if we look at the bubble in a co-moving frame. We see in particular that towards the end of the animation the bubble shape starts to oscillate.
The velocity of the bubble reaches a maximum very quickly and as the cusp is forming it is slowing down a little. The shape oscillations that we could see in the earlier animation correspond to the velocity oscillations after 50000 iterations.