When children had the chin cough their father or mother used to out on the road and the first man they met riding a grey horse they used say to him, "You who ride a grey horse give me a cure for the chin cough". You should do what he tells you. But that custom has died out now.
Old people say if you see a man riding a grey horse, and ask him what would cure a chin cough whatever he would tell you it would cure you.
Go and meet a man riding on a grey horse and do whatever he tells you.
If you meet a man riding a white horse whatever cure he will give you will be the best cure.