Hollywood is addicted to sequels. It's a big-screen trend that bloomed in the '70s, thanks to the Godfather movies.

But it wasn't until this decade that the trend exploded in a jumble of franchises like Shrek, prequels like Batman Begins, "reimaginings" like Ocean's Eleven, and even remakes of sequels, like Halloween II.

All this sequel madness actually started much earlier, NPR film critic Bob Mondello tells Guy Raz. "This is how Hollywood decided to hook people in.

The first place," starting with matinee serials like Buck Rogers. One of the big differences this decade, says Mondello, is the literary roots of many film franchises, from The Lord of the Rings to Harry Potter to Twilight.

And there's another big literary influence these days  comic books like Spider-Man, X-Men and Watchmen. Mondello says the franchise frenzy has even changed the way we watch movies. "What Hollywood does is it cuts off the conclusion," he says. "So you get this rising action to a climax, you stop, and then you're set up for the sequel.