Revealing mistake: Bruce Willis wore fake feet during the movie to protect his own while shooting the film. They were like boots that slipped on over his. At the part where the FBI guy shoots at him from the helicopter and Bruce jumps to a lower level of the roof, you can see the tops of the fake feet that aren't tight around his ankles. (01:50:30)
Continuity mistake: When Maggie starts cleaning up the flour, she hears a noise and looks at the three blue flowerpots, and there is a wooden chair right beside them. Then when it cuts to Maggie getting up, the chair is now about a foot away from the flowerpots. (00:22:50)
Continuity mistake: When the "I LUV YOU" picture is viewed in Nordberg's hospital room, the photo has a vertical/portrait orientation. When Frank shows the picture to Jane, the photo has a horizontal/landscape orientation. (00:12:50 - 00:38:25)
Revealing mistake: When the Blob is eating Paul at the doctors office, his right arm is the only part not covered. It's very obvious that it's in a fixed plastic sleeve surrounded by the Blob's ooze.
Continuity mistake: Near the end when they're entering the Mexican village, Billy's coat disappears as he rides through the gate. (01:17:45)
Continuity mistake: When General Kael takes the baby to Nockmaar Castle, it has an extra 'turret' on the left-hand side, which has disappeared when Willow and Fin Raziel face the castle later on. (01:31:40 - 01:41:15)
Revealing mistake: During the big fight scene, you can tell easily that Frank is wearing knee pads (try looking when his pant leg is wet). Construction workers will often wear knee pads for work but most often they wear them on the outside of the pants to save the knees of their pants. (00:58:50)
Continuity mistake: When Harrison Ford is on the rooftop and the suitcase accidentally opens, the Statue of Liberty goes flying off the rooftop and on to the ground, several stories down. In the next shot, the little statue is perched at the edge of the rooftop. Also, the clothes that fly away magically reappear next to the suitcase a shot later.
Revealing mistake: During the fight montage, the winner of the first match wins by kicking his opponent in the face. His foot never makes contact.
Visible crew/equipment: When two of the characters are driving around the "deserted" town, someone can be seen peeking out of the window of a house. (00:39:11)
Revealing mistake: When Jemma enters the headshrinker's laboratory, there is a table with three heads on it each encased in glass. When it goes in close-up on the middle head, you can see that the table has a hole where the actor can slip in his head.