Sulfur hex is weird ****. It's a fantastic electric insulator but you gotta be real careful around it. Since it's so much heavier than air, when you pour it out it will pool in the lowest spaces it can reach. You can't see it or smell it, so if you went down in a low area full of it you wouldn't know you werent getting oxygen until you blacked out.
The part that always freaked me out was that its so damn heavy you can't breathe it out. You have to stand on your head and open your mouth and let it pour out of your lungs before you can get any oxygen back in there (which I'm sure is what the guy did right after that clip)
I figured out the boomerang. The guy is in space where there is no (little) gravity, but there IS air in the capsule. The boomerang works based on aerodynamics NOT gravity. Therefore, because there is air in the capsule the boomerang comes back. If he were out on a space walk and threw the boomerang it would not come back.