Have it Happen To You Before?

Any idea what this is?  It is a HOLE in my common toilet ceiling!  It happened on LZ's birthdays...  Wonder how the contractor hack the flooring in my neighbour's house and caused this to happen!  AGGRRRHHH!!!   The contractor has the cheek to jokingly tell me they can peep into our toilet!  They definitely can coz we can see through it!!!!

Anyway, because of this and we are also changing the pipe in our house, we have to be out of the house for the next few days....