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The clock seen in the movie is actually a prop clock that was designed to flip back and forth between 5:59 and 6:00. In addition the alarm goes off and plays the song exactly when the clock flips to 6:00. With a real flip clock the alarm can go off randomly around the time the alarm has been set to activate. When looking at the clock on the third day one can clearly see the white curved shapes of the bottoms of the numbers on the previous minute panels.
Bill Murray was bitten by the groundhog twice during shooting. Murray received a course of rabies vaccines, as a result.
According to Director Harold Ramis, most of the time, when he tried to explain a scene to Bill Murray, Murray would interrupt and ask, "Just tell me - good Phil or bad Phil?"
Harold Ramis originally wanted Tom Hanks for the lead role, but decided against it, saying that Hanks was "too nice."
(at around 59 mins) The scene where Phil picks up the alarm clock and slams it onto the floor didn't go as planned. Bill Murray slammed down the clock, but it barely broke, so the crew bashed it with a hammer to give it the really smashed look.
The film was not filmed in Punxsutawney, Pennsylvania, but actually in Woodstock, Illinois (just fifty miles from Bill Murray's hometown of Wilmette, Illinois). There is a small plaque that reads "Bill Murray stepped here" on the curb where Murray continually steps into a puddle. There is another plaque on the building wall at the corner that says "Ned's Corner" where Phil Connors was continually accosted by Ned Ryerson. During the Ned scene the sign for "Woodstock Jewelers" is clearly seen in the background.