The Noise class works precisely like the Odor class, except that it is used for sounds rather than smells. Precisely the same properties are available to customise it. We can continue our illustration by making the volcano the source of a sound as well as a smell:
+ Noise 'ominous sound/rumble/rumbling' 'rumble'
sourceDesc = "Mount Gloom seems to be the source of the ominous rumbling. "
descWithSource = "The continuous bass rumble is punctuated by percussive
explosions at irregular intervals. "
hereWithSource = "An ominous rumble shakes the vast cavern. "
displaySchedule = [1,2,2,4]
The only thing we have done new here is to add a sourceDesc, which you should see added to the description of the volcano when you EXAMINE MOUNT GLOOM.
To illustrate the descWithoutSource and hereWithoutSource properties we'll go back and add a ticking sound to the bomb we buried under a pile of rubble some time back, at the same time expanding what the bomb does when it explodes.
+ bomb : Hidden, Immovable 'unexploded bomb/cylinder' 'bomb'
"It's a fat, round-nosed cylinder with tail fins, on a couple of which
are painted tiny swastikas. "
new SenseFuse(self, &explode, 3, self, sight);
"The bomb explodes, the blast sending chunks of masonry flying in all
directions, one piece of strikes you square on the head. ";
respiratorBox.moved = nil;
cannotTakeMsg = 'You must be joking! '
cannotPushMsg = 'That might set it off. '
cannotMoveMsg = 'It\'s probably safest to leave it just where it is. '
++ Noise 'tick/ticking' 'ticking'
sourceDesc = "It's ticking. "
descWithSource = "The ticking is coming from the bomb. "
descWithoutSource = "The ticking seems to be coming from the pile of rubble. "
hereWithSource = "The bomb is ticking. "
hereWithoutSource = "A ticking comes from the direction of the rubble. "
displaySchedule = 
respiratorBox : OpenableContainer 'small (respirator) khaki bag/box' 'khaki bag'
"The square bag is made of coarse khaki fabric and has a pair of carrying straps. "
bulkCapacity = 4
initSpecialDesc = "A small khaki bag lies in the street, perhaps dislodged from the
rubble by the recent explosion. "
+ gasMask : Wearable 'gas mask/respirator/gas-mask/gasmask' 'gas mask'
"It's an ungainly-looking thing with round glass circles for seeing through
and a kind of cylindrical snout to fit over nose and mouth, all held together
by a black rubber face-mask. "
The descWithoutSource and hereWithoutSource properties contain what is displayed while the bomb is still hidden in the rubble. Once the player investigates the source of the tick by looking in or under the rubble, the bomb is revealed and the descWithSource and hereWithSource messages are used instead. We set the displaySchedule to  to display the hereWith/WithoutSource message each turn, since the ticking can reasonably be expected to engage the player's attention.
Now that we've defined the gas mask, we can (provisionally) define what it means for an actor to be masked:
isMasked = (gasMask.isWornBy(self))