The deep vile self absorption of the characters is balanced by the ridiculous ends they pursue for ultimately selfish goals. The horrific treatment of Addie's coffin, the effects of the water, the heat and the fire create an image that is so uneasy it is only consumable with laughter. Dark humor accentuates the difficulty of the scene instead of distracting from it.
Vardaman is so lost and forgotten that the reader's burden of empathy is too great without some ridiculous humor to ease the pain. Dewey Dell's mission was doomed to be foiled by the exploitation of the next man she encounters, yet she willingly participates. Cash's injuries are so utterly grotesque they provoke a chuckle and a shaken head from the reader.