Okay, this is pretty weird, and it's true. I'm not sure if it was a glitch.. but I swear I saw something. So I started an all new survival world. I got wood, did all the basics, and then began mining with my newly forged wooden pickaxe. I found a little circular dig out that I could settle in. I placed some chests down, a furnace, and a crafting table. I made a mine that goes deeper into the ground after that. With my luck, I found an abandoned mine shaft. I scampered around, gathering everything in the chests placed carefully around the dead ends. After I got the items, I mined a few iron and gold ore blocks. But behind that was ANOTHER cave tunnel. I went down there, and realized I should probably go back up to get more torches. But I was very eager to explore. So I just slowly walked around, checking everything. But then, I saw a black figure run VERY fast through the cave walls. I began to lag. I said to myself that it probably was an enderman. But I doubt it was, because it wasn't thin, and it was player-size. I began to lag some more. Soon, I was lagging so much, my screen went white and it said: "Program "Minecraft" has stopped working.". I clicked "Wait", but then Minecraft crashed. I never saw this figure again.