Two of everything- a couple found a special pot, what is so special about it?

Old Mr.and Mrs.Hak-Tak, lived in a little hut on the side of a mountain in China. They had a couple of fields in which they grew rice, and a plot at the back of the house where they grew vegetables. Apart from a few old pieces of furniture and some threadbare clothes, that was all they had.
If ever they had too much produce, which wasn't often, they would sell it at the market in the village down in the valley, and buy a few things which they couldn't make or grow themselves, like tools or cloth for clothes.
One day, Mr.Hak-Tak was working in the rice paddy when he saw something sticking o…