Yes, the mess is an Area2D. Looking at the code it seems I intended for all sorts of messes, but I think I only had time to do one for the Ludum Dare.
I made the sound effects myself. I think I can do a good "meow".
Great idea with adding an economy to the game! I also thought it would be cute to let the player pet the cats too. Maybe that would keep them from making so many messes or something.