Yu Dong did not care that Ah Cy was upset with her, what she said was absolutely right. When the flood came all the livestock that the villagers were raising were either killed or drowned, the ones that were swept away were not dangerous but the ones that were drowned were indeed a danger to the village.
After being in the water for so long this livestock might have already gone bad but because they still looked edible to some who did not have anything saved, there was a chance that the villagers would still eat them. In case they were to eat those chickens and pigs then the chances of an epidemic breaking out will get even higher.
