I've been feeding this family of 5 crows for years. They have gotten comfortable enough with me that they'll come get snacks while I'm still sitting next to the food. I can call them with a specific whistle I use just for them, and they make a rattle noise (that sounds like the Predator) with me to thank me for food.

One late night I hear this horrible loud screeching. It woke me up, so I ran outside to see what it was. There was a guy trying to break into a window in my house and the 5 crows were dive bombing him screaming as loud as they could. He ran away.

So I guess I have guard-crows now.

Well not quite a perfect fit, but the one that always sticks in my mind was that the Mongolians would always boil their water before drinking to "get rid of the tiny evil spirits'.

That's a pretty good description of germs and bacteria for the time period.