This quick, one-page gag was born after I read a humour article in an early-1940s copy of The Aldershot News that poked fun at some differences between Canadian and British culture (the food, the level of formality, the public drinking, etc.) Something that surprised the British, apparently, was the Canadian men were willing to lend a hand in the kitchen. And something that surprised Canadian soldiers--according to the article, at least--was that English toilets a) flush with a pull chain and b) make a hell of a racket. I thought that to be the exact kind of earthy detail that Two Generals was created to make record of, and a perfectly all-visual cue to capture the feeling of having travelled to foreign country for the first time.
Some people seem to agree with me (like my editors, who always said this was their favourite part of the book.) Others, not so much: I recently received an email from a reader who didn't understand what was going on in the scene and found it "very hard to believe" that two men from Ontario would never have seen a flush toilet. So, to reiterate in case you're having difficulty decoding these mostly-silent panels: it's a PULL-CHAIN toilet, and according to the at least one writer of the era, that was a novelty for Canadians.