What does the laughter symbolize in "The Masque of the Red Death"?

During Prince Prospero's feverish masquerade, the knights and dames dance wildly in gay company until the huge black clock tolls the hour.  Thus, each hour, the dancing stops and the musicians cease to play, and even the "giddiest grew pale" while they listened to its chimes.  Then, when the clock was finished, "a light laughter at once pervaded the assembly [...]."  They are aware that everyone outside the abbey is likely dead or soon will...

During Prince Prospero's feverish masquerade, the knights and dames dance wildly in gay company until the huge black clock tolls the hour.  Thus, each hour, the dancing stops and the musicians cease to play, and even the "giddiest grew pale" while they listened to its chimes.  Then, when the clock was finished, "a light laughter at once pervaded the assembly [...]."  They are aware that everyone outside the abbey is likely dead or soon will be from the Red Death, and the clock striking, knelling away the hours, reminds them of their own mortality, the possibility that they, too, will eventually succumb to death.  This is why their dread grows as the clock approaches midnight, the hour symbolic of the death of day and, thus, of life.  Their nervous laughter seems to be their attempt to shrug off their morbid concerns, for, as the narrator tells us, "security [was] within" the abbey, and these "hale and light-hearted" people are safe from the horrors outside.  Their laughter indicates that they know that they cannot remain so forever, that death can and will come for them when he decides, not when they do.