The piezo-electric ignitor from the electronic lighter is pushed, which causes a spark to jump the spark gap, which ignites the hydrogen and oxygen. The resulting high pressure steam forces the water out through the exit tubes, high into the air. The first few attempts at constructing the bomb. Finally, the wax is melted out of the hardened plaster, and the hollow is filled with molten metal, which cools into the same shape as the original wax model. The plaster is broken away, and the finished piece of art or jewelry is cleaned and polished.
Later versions use a simpler spark gap made of copper wire.
You can also see a rectangular tube curving up from the bottom of the chamber and exiting out the top of the device. This tube was formed from a thin sheet of wax, and is there to let the water in and out of the chamber. There is another tube like it on the other side. The blue at the bottom is a pile of plastic beads that the wax model was sitting on when the liquid plastic was poured over it. The problem with the lost wax version is that you can't see the inner workings very well.