A girl let a goat eat some of her flour, and in return for the kindness, the goat told her there will be a flood. Only she and her brother escaped. After the flood, they couldn't find mates. The goat reappeared and said they could marry themselves, but they would have to put a clay pot with a broken bottom on their roof to signify that they are relatives. [Kahler-Meyer, in Dundes]
or
References: Dundes, Alan (ed.) The Flood Myth, University of California Press, Berkeley and London, 1988.