Since I know them so intimately, I can tell the difference right off the bat. I’ll ask you to notice that Garçon’s head is rounder than his sister’s. I find Pirouette’s bone structure to be more refined than her brother’s. It’s hard to tell from this photo, but Garçon is measurably larger than Pirouette. I’d say he has at least one pound over her. That may not sound like much in human terms, but for cats, it’s a big difference.