I would have said editing once, but I'm coming to terms with it as a chance to enjoy the craft, and a thing to do in small chunks when I don't have the time to get really into writing.
So now it's research. Stopping the flow of writing because I wonder whether a thing is really possible. I want bows to work the way they work in my head, but no, I better look up and find out just how far they can shoot and whether the arrows will penetrate and all that stuff. This includes having to stop to find out whether what I wrote in previous chapters is consistent with what I'm writing now. The best part of writing is getting in a flow state, and everything that stops the flow is annoying.