Oddy has had surgery today, investigations showed a blockage which turned out to be a small piece of rope toy wrapped up in grass with some hair to add to the mix. It was located where the stomach joins the intestine, explaining why there was a mixed picture of food coming back up straightaway to yesterday when it was two and a half hours after eating, and he was poo-ing normally for 2 days. They think it must have been moving through until it finally got stuck, and that the grass eating was his attempt to resolve things himself. I'm relieved it is nothing more sinister.
He's staying overnight in the surgery and we will see what tomorrow brings.