In a 51-second promo for the upcoming sci-fi flick Looper, which stars Bruce Willis and Joseph Gordon-Levitt, director Rian Johnson introduces blink-and-miss-it footage of the film, giddily announcing that fans will get to see more in just three days. No, not the entire film — that doesn't come out until Sept. 28 — but another, longer trailer that premiered Thursday. (Watch both videos below.) That 51-second clip is, in essence, a trailer for a movie trailer. Looper isn't the first film to tease the teaser with a teaser, either; it follows Twilight, Prometheus, The Hunger Games, and a series of other movies. "The trailer launch has become just as big an event as the movie opening weekend," trailer editor Michael Kahane tells the Los Angeles Times. Here, a guide to what some call an "annoying" trend:

Why do trailers for trailers even exist?
While filmmakers have used regular-length trailers for nearly 100 years, they've become so popular that in order to capitalize on fans' anticipation for big blockbusters like The Hunger Games, "studios now market the marketing," says Ben Fritz at the Los Angeles Times. The internet and "rabid fan culture" have turned these trailers (and their baby trailers) into online events "promoted and analyzed as avidly as the films themselves." Studio execs figure, hey, if people want to watch the "trailer for a trailer," we'll give it to them. 

And they're really that popular?
Yes. In 2009, trailers were viewed about 3 billion times. This year that number is projected to increase to 7 billion. The 30-second mini-trailer for the upcoming movie Prometheus (out June 8) simply touted, "In three days, Ridley Scott returns to the genre he redefined..." and the clip has already been viewed 29.7 million times.  

Does everyone like them?
Nope. It's the "most annoying trend" in movie marketing yet, laments Kyle Buchanan at New York. Not only do teasers fake out those who are expecting to see the full-length trailer, but the hype they create comes at the expense of future enjoyment. Fox, for example, assembled a collection of incredibly striking images for its brief Prometheus teaser, but "it sacrificed the full oomph of the [full-length] trailer for all those split-second trinkles." This trend could also lure studios into thinking that teaser and trailer quality is more important than the quality of the actual film, says Brad Brevet at Rope of Silicon. As long as the studio can manage to "build enough buzz to ensure opening weekend box-office dollars," that's all they'll care about.

Do the mini-trailers even get people to watch the movies?
We still haven't seen proof that these "trailers for trailers" are actually getting more people to go see the movies, says Adam B. Vary at Entertainment Weekly. Many of the first films to use these teasers — Prometheus, Breaking Dawn: Part 2 — already have large, built-in fanbases that would show up in droves regardless. The true test will come with Looper or Oliver Stone's Savages, which both employed this strategy but are essentially "blank slates."

The trailer for the trailer:

The trailer:

Sources: Entertainment WeeklyHuffington PostLos Angeles TimesNew YorkRope of Silicon