This is what it looks like when a rat eats through the bottom of the bath trap.
After going to investigate a leak through the ceiling into the kitchen below, we found a very large hole in the bottom of the trap. You can see where the rat has chewed through the pipe to get to the water inside. It is unusual through a trap, but we quite often find where they have chewed through the dishwasher drain hose.
No rat was found but I'm sure it has a terrible tummy ache.