Since we have a fair amount of Irish blood coursing through our veins, the law of Murph seems to be especially potent here. In this case it means the following:
If a cat has to yack and starts out yacking in the middle of the living-room floor (for which you are extremely grateful) the cat will immediately get wind of this aura of gratitude and go pelting underneath the Christmas tree in order to empty the contents of its stomach onto the Christmas tree skirt.
On the other hand, the tree-skirt is probably easier to wash than the carpet, so maybe it's not Murphy's Law in this case.
Remember what Happy Bunny says. "When life hands you lemons, use them to squirt juice into the eyes of your enemies." ^_^