Dennis Hopper plays some of his scenes with an Irish brogue, some without, and others with an indecipherable accent.
Swan was driving a BMW, but the car that was blown up was not a BMW.
In the opening section where Seagal's team abseil from the helicopter into the house, the helicopter changes. When we first see the team they are in a Bell206 (Long Ranger); this has skids and no stubbed wings. Yet when they abseil down the helicopter is now a Bell222 which has a retractable wheeled undercarriage (no skids) and stubbed wings.
After Sizemore and his partner are discussing the fate of a "call girl" in the drug bust scene, Sizemore handcuffs the accused. In the next shot the accused is lying on his stomach on the floor with his hands behind his back, however, there are no longer any cuffs on his wrists.
In the opening explosion, a policeman is hurled through the air towards the windscreen of a parked police car. In a POV shot through the windscreen, it is noticeably cracked & smashed in the position the policeman is due to hit it BEFORE his impact.
The movie supposedly takes place in San Francisco, yet, at least twice, Illinois license plates can be seen on cars. The film was initially set in Chicago before the change to San Francisco.
When the bar gets blown-up you can see that one of the emergency vehicles has Florida license tag on it.
Just before Swan calls to say to drop it off at the museum, there is a random shot of San Francisco, which is followed by a random street scene in New York City.
When Segal is asked via walkie talkie how his bomb disposal activities are proceeding, he checks the digital bomb display, then responds by saying "One minute and 42 seconds remaining". The camera then pans to the bomb display which clearly shows one minute 46 seconds remaining.