The recent announcement that producers plan to make a sequel to "Piranha 3D" seemed to make little sense.

After all, the movie made a paltry $10.1 million on its opening weekend a few weeks ago -- coming in sixth on that week's box-office list -- and only $18.2 million as of Sunday. Despite some critical acclaim, it looked like a bomb.

But then the logic of sequels isn't always apparent.

Take the "Resident Evil" series, about hottie Milla Jovovich battling zombies.

The fourth film in that franchise, "Resident Evil: Afterlife," is due Sept. 10. And yet not one of the previous "Resident Evil" movies has been a smash hit, the biggest barely topping $50 million domestically.

The key word there is "domestically."

Because while the previous "Resident Evil" film -- "Extinction" -- made $50 million in North America, it brought in an additional $97 million worldwide. Thus the sequels.

Obviously, the producers of "Piranha 3D" figure that folks outside the United States will enjoy seeing swimmers being eaten by toothy fish. Beyond that, the film already has the smell of a cult fave, so DVD sales could be healthy.

So "Piranha 3D" might eventually turn out to be a bomb and a hit.

Or just a bomb -- and the announced sequel will never actually get made.