Villano said:
One day, he and the guy he was working with were having trouble with the film they were working on. The movie was so bad, they were having a difficult time trying to make an exciting trailer.
Finally, as a bit of a joke, they edited in an exploding helicopter from another film. Surprisingly, it looked like it fit in the movie, so they left it in.
Eventually, it became a running gag. They inserted that same helicopter explosion in every single trailer they cut from that day forward. And the funny thing is that it always looked like it belonged.
Ah, so THAT explains the exploding helicopter in the Two Towers trailer!
Hong "don't tell me you didn't see it, people" Ooi