@ChrisChris Ohhh, these splits, circled in the attached image?
That's the very last step before it goes in the oven. I score them in with a serrated knife. The method is pretty much https://www.youtube.com/watch?v=tp5H87Su1jE except I flour, rather than oil, the worktop for kneading.
In the video, Paul talks about these slanted cuts providing a distinction between the floured and unfloured parts to make the thing look attractive; but I've wondered if they're also doing something physics-wise, essentially giving it a screw-like structure to help it rise more upwards (rather than uniformly outwards).