"Too much contact with non-Yazidis is also considered polluting. In the past, Yazidis avoided military service which would have led them to live among Muslims, and were forbidden to share such items as cups or razors with outsiders."
I wish Christians had a similar rule so Muslims could get a taste of their own medicine. Just for the Luz.
Yazidis do not believe in the devil. Shaytan is the name of an angel (leader of the other angels, God's representative on Earth)