This is a collision between three water droplets.
The first is the one that is travelling upwards in a spike known as a Worthington jet.
The second droplet has fallen onto the Worthington jet and almost shattered into that array of spreading arms many of which are terminated by small bubbles.
The third droplet, timed to fall some twenty-five thousandths of a second behind the second droplet, has just broken on the tip of the Worthington jet creating that transparent cap.
All of the timings for this image – the triggering of the camera, the release of the three droplets and the firing of the flash units, were co-ordinated using the Arduino microcontroller and additional cicuitry described in a previous blog entry.