One of the commenters on the video thread had this to ask:

After the surface of the water drop merges with that of the water contained in the glass, why is the remaining drop projected upward? Where does the force for this come from?

Another one of the viewers replied:

Surface Tension, when particles are effected by Buoyancy in which they defeat the thrust of gravity, combining each-other at the surface of the water, leaving smaller and lighter particles to be lifted on top, as tension by densities.

We hope you like the video and thanks to the Slow Mo Guys!