Whether it's being used to cover up an unwanted moustache or create an entire character from scratch, dodgy CGI is a filmmaker's bane. Ropey digital effects have the potential to shatter audience immersion and turn a movie into a laughing stock.
Many Hollywood blockbusters have been shot in the foot by their own FX department and the problem isn't always a lack of budget. Indeed, some of the ugliest CG abominations ever created have crawled out of the biggest studios in the business.
This issue is particularly prevalent where superhero movies are concerned, as CGI is often essential to convince the audience that a man really can fly, or run faster than the speed of light, or even swing across New York like an oversized arachnid.
When the film industry's special effects gurus play their cards right, the illusion can be seamless and the punters leave the theatre filled with a sense of awe. But when they get it wrong, the whole thing collapses like a house of cards... and that isn't a reference to Kevin Spacey's career, in case you were wondering.