The scholar's stone. *SPOILERS*
So it floated in the flood scene, so it's probably a fake I assume. Did the friend Min know it was a fake or did neither he or his grandfather recognize it was a fake themselves?
I'm just curious if the director was trying to convey that Min thought the Kims were ignorant and wouldn't notice or that he himself was ignorant and couldn't tell a real rock from a fake? (if that makes any sense)