Visible crew/equipment: When Jackie Chan is standing on top of the tower, and shouts "Who am I?", the camera starts to circle around him. When it does this, you can clearly see a guy in a white shirt standing underneath, and then hides away in the corner! It's really clear to see.
Visible crew/equipment: When the lab where the scientists are starts to blow up, if you watch closely on the table where the scientists are running from, you'll see a pipe which is blowing out sparks into the air to make it look like it is blowing up!
Answer: It's quite possible because most movies use dubbing (or "looping") as part of the post-production work to enhance the quality or fix minor sound problems. Sometimes a different actor's voice is dubbed over a minor on-screen character.
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