At Christmas 1914 soldiers left the trenches to shake hands.
Along several sections of the Western Front at Christmas 1914, German and British soldiers spontaneously stopped fighting. They sang across no man's land, swapped cigarettes and food, and buried the dead; a few accounts mention football games. Commanders later banned such fraternization strictly. In 1915 there were only a few cases, by 1916 almost none.
Useful: Enemy images hold up poorly once people meet face to face.
Source: en.wikipedia.org