the sound of fear

shawn (phd student in my lab) and i were sitting at the computer working on some data analysis the other day, when suddenly we hear a loud "BANG":

shawn: that scares me
me: why?
shawn: cause what just fell was one of those big air tanks. if something pops the valve or punctures that tank, the compressed air will send the tank flying for miles. i've seen it blow through concrete walls before.
me: holy crap.... and this guy is like 2 feet from us on the other side of this wall.

(BANG)

me: ok, i'm starting to get a little scared now.

(clink....clank.....bang)

me: does this guy know about the dangers of throwing around compressed air tanks?
shawn: let's just hope he's got the cap on the correctly, cause otherwise, that's beyond dangerous.

(screw....screw....screw)

shawn: well, there's the cap going on.