I was getting attacked by a big group of Drowned, and among them was a Drowned Chicken Jockey, which I wanted to preserve for a screenshot. While I was fighting the rest of them, I kept taking damage when there was nobody near me, and I kept looking for any Drowned wielding a Trident, or any other ranged mob that could have been hitting me, but there was nothing there. Once I clearded out the entire group and only the Drowned Chicken Jockey was left, I got up close to take a screenshot, but I still kept getting hit. I also noticed that the baby Drowned kept turning it's head away in weird directions. Eventually what happened, is the baby Drowned randomly died and it's experience and drops popped out right next to me, when I was a good 15+ blocks away from where the actual mob had appeared to be, but the chicken stayed right where it was the entire time. It turns out that what was hitting me that entire time was the baby Drowned that I was looking at, but on my screen there was nothing there and the mob appeared to be completely stationary, only rotating and turning it's head, presumably in the direction that it was supposed to be facing when it was attacking me, and it eventually killed itself on my Thorns enchanted chestplate.