One of the magical special effects from Disney's movie "Pirates of the Caribbean: The Curse of the Black Pearl" involves a transformation that occurs when the cursed pirates step into the moonlight: Their wicked nature reveals itself as they become skeletons.

It's all about image and illusion.

Creating that effect was a lot of fun for Hal Hickel, animation supervisor for the film. But it was tricky, as well, he said during a telephone interview from his California office, where he works for the company that did the movie's special effects, Industrial Light & Magic.

The action moves from live performers to computer-generated skeletons in the blink of an eye, and the mannerisms and movements all had to match. "Geoffrey Rush (who plays the ghostly Captain Barbossa) is a great actor, and you enjoy watching his eyes," said Hickel. "You can't just change to skeleton without getting that same spark of life behind his eyes."

The special-effects crew, under the direction of John Knoll, also had fun building miniature ships and blowing them up on giant water tanks and making it all look very much like the ocean. They also worked on other effects, but are most proud of the skeletal work.

Animatronics were first used in the Disney ride, director Gore Verkinski explained in the movie's production notes. The barking dog and the talking skeletons made visitors wonder whether they were real. But because today's audiences are savvier about special effects, the movie crew turned to computer-generated animation to achieve that same kind of reality.

Hickel said he believes the film takes animatronics to a new level, as they were able to capture the look and feel of the actors so that, even as skeletons, you know which pirate is which — not just from their voices, but from their appearance and movement, as well.

The complicated process began with taking photographs of the actors in wardrobe and makeup. Then a skeletal painting was made of each one. That was followed by 3-D scans of the actors. One detailed skeleton was built with all its real bones in place. Then to take into account all the differences in each actor, the skeleton was "scaled and smushed" into each 3-D scan.

Once they had their skeletons, the next challenge was putting them into action. The fight scenes where particular tricky. They would shoot the live actors, explained Verbinski, and then pan over to a skeleton that wasn't there. They were essentially photographing air, "which looked pretty silly by itself," he said in the production notes. But the crew made it all work. And he added, the skeletons "allowed us to have even more fun with the genre and the characters."

"The skeletons weren't in the original script," said Hickel. "When the writers (Ted Elliott and Terry Rossio) came on board, they brought in the supernatural element."

It has been a lot of fun, Hickel said, to work on a film where everything "came together so well." And to work on a pirate movie.

"All of us who did this grew up on the films of Ray Harryhausen, who pioneered the mixing of live action and stop-action animation," he said. "Films such as 'Jason and the Argonauts.' And we all grew up with the romantic view of pirates that Hollywood has given us. So, all along the way, the excitement level was high."