I know in Animal Crossing: Wild World, if you put too many things on the floor in a room, the floor would give out. Does the same mechanic exist in Animal Crossing: New Leaf?
The floor does not actually collapse in either version. Instead, after 24 items have been placed in one room in Wild World or 48 in New Leaf, the game will not allow you to place more. The ingame text in Wild World gives "the floor will collapse!" as the reason for allowing no more items to be placed. I don't know what the equivalent text in New Leaf.