What, you mean they aren't supposed to be there
...anyway, it's a rather interesting experience when you're doing a watch shift in a cold and rather dark forest - not too dark, just so that you can't really make much of what you see but not pitch black either. After a couple hours you actually start seeing movements and almsot-human-shapes in the forest. And that's a fact, no kidding (no [additional] chemical stimulus either). You just need to wait for long enough for the visual system to start throwing some kicks in the mix to break up the monotony, and they do such fabulous job that it's sometimes a bit disconcerting. Not exactly scary after you know what goes on in the back of your head, but not exactly pleasant either.
Try it, you'll love it.
The scientific explanation is basically just that. Human brain - especially when it comes to eyesight - tends to make out patterns from where there are none. And since human shapes and especially faces take a *lot* of processing area on visual cortex (and beyond), the random activity in cases when there's nothing to see will cause you to think you see some shapes, and the face recognition part of visual processing area being a big one, those shapes pop out quite fast in cases like this.
Like, for example, does this look much like a face to you?
It's a yellow ball with two dots and a curve on it
, it's not much of a face. But people still register it as a face. Hell, even if the line's not curved you'll accociate it to a face. You'll even think you can see some emotion on the face, like boredom.
Even more interestingly, people can correctly identify the owner of a face from surprizingly little amount of information
Squint your eyes a bit or step back, look at the picture and take a guess who it is.
It's obviously Sean Connery.
Ummm... where was I?
Oh yeah... so, there will definitely be moments when the nebula thingamaroos align themselves to resemble something like faces. Whether you register it or not is the question. In a moment of boring escort flying it's more likely than in the heat of the dogfight I'd guess.