Another question that's recently crossed my mind while playing: under what circumstances do Nightopians actually die? While blasting through Spring Valley over and over to practice the bosses, I've noticed that the Nightopian population fluctuates but always stays about the same - roughly 30 critters according to the Nightopian Collection - even though I'm usually opening four to six eggs each time I go through the level. So this means that Nightopians must be dying about as fast as new ones are being born, though I don't think I've read anything about Nightopians "dying of natural causes" before, at least not at such a fast rate.
I know 30 isn't a definite maximum for the game, because I have a constant 40 critters in Soft Museum, so I suspect it's because all 30 of my Spring Valley Nightopians are clustered in one part of the level - the big tree at the end of Course 2 / Course 4 and the hill to the right of it. Now if the game didn't keep a limit on this sort of thing, and the Nightopians never died, I'd eventually end up with a ridiculous amount of Nightopians on screen that would slow the game down to one frame per second, so it makes sense that they're being culled in some way. I'm guessing that the game periodically checks how clustered your Nightopians are, and kills some off when necessary to make sure that things don't get too silly.
Also, while flying through those courses I often hear the "egg laying" noise that Nightopians make when there's apparently no eggs being layed; with all the Nightopians being in one spot, I can check this pretty easily. My suspicion is that this noise signifies both Nightopians being born and Nightopians dying, though I'm not 100% on this.
However... sometimes while playing I actually hear the Nightopian "scream" noise - the one a Nightopian makes when you paraloop it to death - when I'm clearly not killing any Nightopians myself. This only happens quite rarely, but what causes it? I vaguely remember at the back of my mind reading that level enemies can actually kill Nightopians if the Nightopians stray too close to them; is there any truth in this?
... Talk about kinky. XP
I wish some of my pians would get eaten. There aren't too many of 'em yet, but I'm a firm believer in a controlled environment when it comes to performance of an awesome game.