For all the talk of the talking in director Peter Jackson’s First World War documentary They Shall Not Grow Old, it’s a scene in which those featured in the film don’t say anything that resonates perhaps more than any other. It comes at the storyline’s transition from the war’s outbreak in 1914 and the enthusiastic queues of volunteers and recruits-in-training, rendered entirely in restored black-and-white, to the battlefront trenches of France, where the old footage emerges in full-colour, its detail and currency jarring to those who’ve only seen the time through the filters of scratched and faded monochrome. There is a line of Tommies wending their way through a trench, at the middle of which shuffles a uniformed boy not more than 15 or 16 years old. He is staring straight into the...