It might be a thundering starship or a majestic steamship, a flower that blossoms before our eyes or a flock of geese taking flight on cue, a well-trained owl or a hungry tyrannosaurus. Or it may be a throng of ecstatic soccer fans or a solitary ghost. Sooner or later, the need will arise for a moment that is too difficult, too expensive, or simply impossible to shoot in real life. This is when a filmmaker turns to visual effects.