Revealing mistake: When Clark's sneeze launches the bowling ball, the ball casts no shadow, revealing it's a superimposed image.
Revealing mistake: When the firemen's truck runs out of water there's a close-up of the level meter and it reads "Pierreville fire trucks Ltd. Camions a incendie" revealing the scene was shot in Canada.
Answer: There were rumors that Hackman was angry with the Salkind Brothers (the producers) for firing director Richard Donner, though Hackman later disputed saying that. His explanation, though he may have been downplaying the real reason, was that he had a number of other movie projects at the time, and he also did not wish to continually play the same villain in an ongoing movie series.
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