What's real and what's fake? A guide to movie F/X

MEN IN BLACK II

THE SETUP Frank the pug wasn't the only creature to get mouthy in ''MIBII'': Jeff the worm, an all-CG ghoulie, menaces Will Smith's Agent Jay during a subway ride. Director Barry Sonnenfeld collaborated with the creatives at ILM.

BEFORE The team started with a basic Jeff model and then kept refining it. ''Barry wanted it to have six rows of teeth,'' says animation director Tom Bertino. ''And they needed to rotate in different directions.'' Sonnenfeld also knew he didn't want Jeff to patter forward on inchworm feet. ''We looked at elephant seals throwing themselves at cars. It's a living.''

AFTER The toughest part was Jeff's mouth, which swings open at four places. ''He can hinge to the bottom, to the top, and to the two sides simultaneously,'' Bertino says. ''That's properly creepy.'' The final shot was a three-in-one deal: Footage of subway tracks formed the base; over that was placed the CG Jeff; and finally Smith, shot on bluescreen. The action of Jeff opening his mouth was ''dirtied,'' so that all four hinges didn't open at once. ''That's what makes it believable,'' says Bertino. ''If you can believe in a 600-foot bag of suet running through a subway.'' --Gillian Flynn