My father was a veteran of WWII, in the Finnish army fighting the Soviets. In (I think) 1972, I was a 6-year-old kid, and we went to the town 60 km away (we di

My father was a veteran of WWII, in the Finnish army fighting the Soviets. In (I think) 1972, I was a 6-year-old kid, and we went to the town 60 km away (we did not go there very often). Suddenly, my father exclaimed "Hei yks!" (Finnish for "hello one!") to a man on the street. Then they greeted and spoke quietly for quite a while. I didn't understand it at all. Only much later I realized that the other man was a brother-in-arms of my father, and "Hei yks!" was the shibboleth of their unit; it had been devised for a night-time attack in very extreme conditions in February 1942, and the men in the brigade then used it throughout the war to identify each other whenever there was no mission-specific one defined. Russians cannot very well pronounce the y in "yks" the way Finns do. (This was of course no strong guarantee because the Soviet army had some native Finnish-speakers, but most were not.)