A lot of Irish boys fought on both sides, and there's a famous story about thousands of troops camped on both sides of a river the night before one of the big battles - sorry I can't be more specific but American history isn't my strong point - and the boys on one side started to sing a plaintive song called "Ireland, Boys, Hurrah", which starts "Deep in Canadian woods we've met, from one bright island flown, great is the land we tread, and yet our hearts are with our own..."

When the lads to one side of the river finished the first chorus the sound of the boys on the other side, and in the other army, plaintively finishing the same verse a line later, as happens when great masses of people sing together.

The next day most of those boys were dead.