adding a tiny piece of Sodium metal to plain water

the hissing is partly the water boiling due to the high temperature and also the Hydrogen gas being released. A larger piece can create enough of each to catch fire, it's an expensive metal and difficult to get so I will do a bigger peice when I have properly setup the studio lab.
note: look how the piece randomly moves, this is like Brownian motion and is caused by the energy release and the water molecules and impurities causing resistance, this is how most propulsion works...evergy pushes against resistance and as momentum is conserved something has to move to re-balance.

2Na + 3H2O = 2(Na+ OH-) + 2H2 (in pure water)
Sodium plus water makes Hydrogen Gas and Sodium Hydroxide solution (ions)