Reversed bullets

This, from the orders given to the 1/18th Battalion, London Regiment (London Irish Rifles), on the eve of the battle for Loos, 25th September 1915:



Battalion orders

"All men should be warned against probable misuse of white flags and signs of surrender by the enemy. The enemy have been known to sham death and then shoot into the backs of our assaulting troops. Officers are reminded of the procedure of dealing with prisoners found with expanding or reversed bullets."

I know it doesn't actually say anything, but you know what they mean, right?