When Cole and Campbell are walking by the movie theatre, Cole is not wearing gloves. When he shows Campbell the airline ticket, he is wearing one black glove. (This is a reused insert shot from earlier in the film, when Cole was wearing gloves while examining the ticket in the Roslov house.)
When Cole is fighting with Donald at the end of the movie, a wound on Donald's forehead disappears and reappears between shots.
Johnny Strong, who plays Johnny Deverell, is listed in the end credits as playing "Johnny Deverall".
When they are supposedly meeting an informant, the wipers of the car are only working when viewed from the inside, and not from the outside.
When Cole goes to visit Smith in the Restaurant, the place is called "Marcus's". However when the maitre d' answers the phone, and later when Cole answers the phone, they refer to it as "Linto's".
When Cole is talking about the dead woman in the autopsy room he says he thinks he's "Russian, most likely Georgian." Russian and Georgian are two distinct nationalities and ethnic groups. The fact that Georgia was at one time part of the Soviet Union does not make Georgians and Russians at all related.
During the polygraph test, Cole is fingering and stroking a string of beads. This is a relaxation technique that would never be allowed during a polygraph test for fear of giving inaccurate results.
There is no blood or tissue on the breast implant removed from the corpse. It is perfectly clean.
When the fake IAD detectives come to Cole's home (time mark ~1:01:00), they declare "you're under arrest" but fail to handcuff him. Even though he is a LEO, it is impossible that officers would not place a homicide arrestee in handcuffs for their own protection.
When Cole grabs Johnny as he jumps through the school window, there is another window across a gap that is high up, which would mean that the two would go tumbling to the ground, yet Cole and Johnny fly across this huge gap and land through the window on the other side, a physical impossibility.
When Campbell is fighting Donald in Campbell's apartment, Campbell is knocked into his TV, which falls off a short table onto the floor, and sparks are added to the scene with a spark gun nowhere near where the TV fell, and there is no way a TV would emanate sparks from such a short fall, let alone any sparks at all - TVs just don't do that.
When Donald gets thrown through a window barred with heavy iron fencing, the iron clearly wobbles, as if made of rubber.
In the first major fight scene against the Russians, the last opponent Jack Cole fights and eventually kicks off the side of the raised cement floor, the same footage of a hand strike to the opponents head is looped and the same strike (camera from behind Cole's left shoulder facing opponent tangentially) is repeated 5 times. A kick from a slightly more distant angle is re-used twice. This is particularly obvious when slowed down and viewed frame by frame, but also apparent at actual speed due to the fact they keep instantaneously 'retreating' and then moving closer to the edge of the floor/ledge area.
When Cole is taking the polygraph test you can see the female detective is standing on her very visible mark on the floor.
During the end fight scene, Cole says "boring", but his mouth does not move.
When Campbell is shot and the force pushes him out of a window, Cole comes to save the day. After rappelling down and grabbing on to Campbell, a safety strap is shown on their line. In the next shot, you can get a quick shot of a hand pulling onto the line from a nearby window.
Before the final confrontation between Jack, Jim and the bad guys, there's a glimpse of a hand pulling the red sofa backward when Frank, Donald and the rest of the gang are entering in the hotel room
The microphone can be seen in the first scene, and while they are watching Casablanca (1942), also later when Deverall and his henchmen enter the Ovington Arms hotel room, Donald locks the door and you can see the boom mic.