Raiders Of The Lost Ark (1980)

Raiders Of The Lost Ark began with a modest 20 million dollar budget, but it became the highest-grossing film in 1981. Starring Harrison Ford, Karen Allen, Paul Freeman, and Ronald Lacey, it follows the characters on their quest for the Ark Of The Covenant.

The “bad guy” Bellock, played by Paul Freeman, is giving a speech when in hot pursuit of Ford.  During filming, a fly perches itself perfectly on the side of Freeman’s mouth, and as it scurries in, Freeman has no choice but to keep filming.