OK, pardon my stupidity. Which of those is a MIG welder? That's what I have been studying in online tutorials, but obviously not studying well enough! He was watching from quite a ways away, but then the welder offered him a chance to try it, and he put on a full face mask thing, as well as big heavy gloves.
Thanks for your help, qwerty; I think the zzzz sound is the one I've heard before!
MIG welders are a sort of arc welder; one feature about them that stands out is that the operator uses a sort of device that looks almost like a squirt gun on a hose. The tip releases a metal wire that vaporizes in an electric arc so you have a continuous stream of molten metal coming into the weld area, along with a shielding gas. You can sometimes hear a bit of a hissing sound from the gas along with the much louder sound of the arc.
MIG torches make good general purpose welders. You can get versions that will weld most metals, they're pretty easy to learn, and they put down a fairly strong weld pretty quickly. They're not quite so good at really intricate, tiny welds.
The welding helmet you wear with a MIG torch covers the entire face and only a small section of it is transparent. The face shield is so dark that, as RJK noted, you can't see out of it when the torch is off. (An oxyacetylene torch lets you use a less dark face shield - you
can see out of those welding goggles.) Most welders these days use auto-darkening helmets that change their darkness level when the torch is on.
If you're welding for a very long period of time with any arc welder, the UV light from the arc can give you sunburn. Many professional welders leave no skin exposed any place they could have light from the arc touch their skin, but welding for a few minutes does not present the same danger.
