It could be something that keeps happening recurrently, or an especially spooky thing that's happened once.

  Here's my story: I haven't played 100% singleplayer minecraft since January-February 2013, but BOY, I was an absolute noob because I pretty much refused to read guides other than crafting recipes that I really, really needed. I basically lived on an island all alone and I literally didn't see anything besides a bat (it could have been a whole week, but I can't really remember lol). I was also in peaceful mode (I got blown up by a creeper and I wasnt about to go through that again), so that meant my world was almost totally empty of animals.
  Eventually I got tired of the island and left. At this point, I definitely didn't know how to use a boat, so I just SWAM my square backside to a desert, where again, there were no mobs. I was enchanted because I had NO IDEA minecraft had deserts until just then, and I made my house out of glass.
I got bored of being all alone in my house after awhile so I decided to go look around because I heard that the game had sheep. I had largebiomes on so I had to do quite some walking to leave the desert and encroach on the taiga.
For some reason meeting my first sheep was absolutely otherworldly and scary because I had never seen anything like them in any game I'd played and they moved so bizzarely. I swear nothing in minecraft is as startling as when I had found my first sheep. I'd played all sorts of stuff before, like Skyrim and Fallout and Half-Life, but all of the deaths and horrifying creatures cannot top the way it feels going from rather realistically animated games to minecraft and having a post-apocalyptic "last-person-alive" sort of solitude broken by a big square beast baaah-ing at you.