User blog comment:Mrob27/The moat experiment/@comment-4829477-20120210141606/@comment-4583259-20120211230202

I haven't tried the "save and re-open" technique but I'm sure it works well, many others report that it does. I think I get more mobs of all kinds if I repeatedly walk long distances back and forth. I know for a fact (based on my analysis of the saved files) that mobs "freeze" (stop moving or changing) when you are far away from them. Maybe the walking long distances makes them spawn, or maybe it's just a coincidence (the mobs were created when I saved and re-entered the game but I didn't notice).