You head home, getting occasional stares at your tail, not that you care. After getting something to eat, and practicing how to sit and sleep with a tail, you find you need to pee, so you go to the toilet.
Little did you know, the chemicals and magic responsible for your new appendage had been filtered through your kidneys and into your bladder. When you flushed, it had been sent through the sewers to the water purification plant, where the magic concealed the presence of anything odd from the filtration systems. The water was then piped into a local resevoir, contaminating it.
So the town slept, with no idea what was happening. The only strange thing was the rats of the sewer had larger tails, and were slightly coloured.
Something tells me we haven't reached the tail-end of the story...