The following can be fun too: Fill a vessel up with salt water. throw
in two carbon rods connected to a car battery charger.
Run it a while till most of the chlorine has gone out.
Power off, put on a lid, hide behind a wall, power on and run the
generated gass into a SMALL baloon. Power off when 5" diameter.
Use a light plastic lid that will pop off and not hurt anyone if the
gas in the vessel ignites.

Then hold the baloon at arms length, close your eyes and take a match
to it. Do it with your hair wet, in wet smim trunks next to a swimming
pool so you can jump in if you catch fire. We had great fun with this
as kids. It is not unbearably loud but generates an incredible bang
and you feel a heat pulse similar to what you get when you set off a
large photoflash right against your skin.