Director Mark Pellington, who did the voice of Indrid Cold, occasionally added his voice under the dialogue of characters who spoke on the phone with John Klein throughout the film. Pellington said the intention was to create the illusion that Indrid Cold could be any one of those people, and that the entire situation and all the people might actually be in Klein's head.
For the masterful "Bridge Collapse" sequence, it took Gene Warren III and five other model-makers, plus two production assistants three full months to fabricate every piece of the bridge set from scratch. He estimates 20,000 individual pieces of steel went into the construction, in order for the ultra-photo-realistic 1/6th scale model suspension bridge to support all the model vehicles and ultimately collapse like a full-scale steel bridge into the water. Of the hundreds of sets Gene has accomplished, this remains his favorite. The entire set was built spanning the water tank at Fantasy II.
The studio cut $2 million out of the film's budget just days before shooting began. Director Mark Pellington was furious, having vowed not to make the same concessions that plagued his previous film Arlington Road (1999).
At the end of the film, it states that the cause of the bridge collapse was never determined. The real Silver Bridge is known to have collapsed due to a failure of eyebar 330 on the north of the Ohio subsidiary chain just below the top of the Ohio tower. The failure of a single eyebar brought the bridge down due to lack of redundancy in the design of the structure. Traffic loads far exceeded what the bridge was built to carry.
The Mothman's face appears six times in the film. The first is of course when he flies into Mary's face. The second is at the end of the scene where John is talking with the woman who saw Indrid through the window, the camera zoom out, and the scorch mark at the trees back left by the mothman has his face. The third is when the young couple describes the incident at the factory site, when the mothman moves off the car. Fourth is in the beginning of the zoom out from Mary's photograph after John had smashed the phone, the mothman's face and shape appears in Mary's pupil. The fifth is when he is seen in the mirror on the door that John slams. The sixth and final time is when the cable slams into the car windshield.
When Richard Gere has first encounter with "Mothman", it results in fatal car accident when his car collides with a tree. The street is Bartlett St. in Squirrel Hill in Pittsburgh, PA. The traffic signal they're approaching was put in for filming and is no longer there.