I did not find a duplicate of this so I hope I'm not duplicating. On one world I had I opened it up and there was a huge amount of animals. I had noticed this on some of my other worlds so I wasn't concerned. Then I noticed steak and leather had popped up in my hotbar. I assume that that was because It was on the ground and I picked it up, but then a sheep caught on fire. I had seen many animals and dropped animal items burning or burned. The weird thing was there was no lightning, no lava, no open fire, but they were random.