As an Aussie schoolkid I remember learning about the ANZAC retreat from the trenches in Gallipoli after hacking together a way to fire their rifles using dripping water, and I always thought that was pretty neat:

"Invented by Lance-Corporal William Scurry, 7th Battalion, AIF, these ‘drip’ or ‘pop off’ rifles fired at intervals to convince the Ottomans that the Anzacs still occupied their trenches.

The drip rifle incorporated two ration tins. The top one was filled with water, while the empty bottom one was attached to the trigger by a piece of string or wire. Before leaving, a soldier punched a small hole in the upper tin to allow water to trickle into the lower one, which eventually toppled over, pulling the trigger.”

https://nzhistory.govt.nz/media/photo/drip-rifle-gallipoli