Get the wind up/to be windy

Is to be afraid in a cowardly manner dates from the First World War. Eric Partridge maintains it derives from the WWI marching song The British Grenadiers. The troops changed the words of these songs all the time and Partridge quotes them as follows. “Father was a soldier at the battle of Waterloo. The wind blew up his trousers and he didn’t know what to do.” From this, to get the wind up came to mean very afraid. A more basic explanation is the involuntary excretion of gaseous waste matter from the digestive system when mortal fear is experienced.