Random Observation for the Day

So today I had to dig through my apartment "move in" packet to find my landlord's address. I noticed this interesting tidbit in there:
"Hint: Don’t ever put these down the disposal:

                        Fibrous vegetables - raw carrots, celery, broccoli, etc.

                        Thick starches - rice, pasta, noodles

                        Peelings of any kind - potatoes, carrots, onions, apples, bananas, melons

                        Rocks from fish tanks"

...

...

Rocks... from fish tanks?

Okay, who dumped their poor fish down the food disposal???