There is certainly a random element to it, however. For instance, from Predator:
The Predator: "Right, well, I'm in the mood for a hunt! I think I'll go... to... earth! Yes, that'll suffice. I'm sure there will be plenty of muscle-bound Austrians with comical accents who, despite having done nothing at all to piss me off, will be unlucky enough to find a place on my trophy wall. It's great being an intergalactic wanker!"