Continuity mistake: During one scene, Mel Gibson is talking to the young boy through the treehouse door and holding the boy's jacket. The next scene, there is no jacket and then it magically reappears. (00:35:30)
Continuity mistake: Daniel grabs Nat's jacket when the freezer gets opened, and it tears visibly and audibly. When Claire sees Nat wearing it after he has found it (that is after Daniel has given it back to him) there is no sign of any damage. (00:28:15 - 00:47:20)
Continuity mistake: In the first scene at Jake's diner, when Daniel fails to propose to Helen, the curls over his forehead change alternatingly from shot to shot. (00:11:55)
Plot hole: When Daniel is in the air with the stolen plane from the Los Alamos air base Nat suddenly appears from behind. However, Nat had no chance to slip into the plane secretely as there was only one stepladder that had been in his mom's full view while she hugged Daniel good-bye. (01:25:30)
Continuity mistake: When Helen and Daniel are lying on the carpet her shoes are placed next to the sofa. When we see them from the front there is only one shoe, although both should be visible from that perspective too. (00:07:30)
Continuity mistake: When Nat and Claire's doctor boyfriend eat Claire's very well done steaks, the amount of juice in Nat's glass changes from shot to shot. And in the last shot of the scene, when Nat looks at the doctor, his hair is neatly combed to the side, in contrast to the mess it was before. (00:22:55)
Continuity mistake: When Helen has the accident in the pouring rain Daniel leans over her to hear her heartbeat. When he lifts his head Helen's formerly open and drenched jacket is closed and dry. (00:15:05)
Factual error: In the scene where Daniel is flying the B-25 (Mitchell) to see Helen, you can see the propellers are turning much slower than needed for a cruising flight. Also, the sound of the engines is too low and keeps changing even though Nat and him are talking.
Continuity mistake: When Finley talks to the drunken Daniel 6 months after Helen's accident, Daniel's head is leaning against the wall or bent forward alternatingly, depending on the camera angle. (00:17:40)
Continuity mistake: When Daniel is making dinner Nat sits at the table, his hands either on the table or folded at his chest in alternating shots. (00:54:25)
Continuity mistake: Daniel comes back to the diner where he failed to propose to Helen 50 years ago. He sits at the same table, and when the camera shows him through the window you see the tip of a ketchup bottle that hadn't been there in the inside shot. (01:00:50)
Factual error: In the scene where Daniel is taking off with the "borrowed" B-25 (Mitchell), they have two shots switched. It shows him taking off (a beautiful shot), and the very next shot it shows him adding power through the throttles. This should be reversed.
Continuity mistake: When Daniel takes off from the Los Alamos air base the FBI and air base guys run after the plane. They almost run over Claire, but when the camera angle changes to a front view of the running people Claire isn't there anymore. (01:24:05)
Continuity mistake: After his fight with Claire's ex-boyfriend Daniel has a bandage on his hand till the very end of the movie, except in one shot when he slips under a plane at the airshow. (00:51:25)
Continuity mistake: When Claire's nasty ex-boyfriend gets beaten up by Daniel his nose is bleeding. However, in the next shot the nose is clean again. (00:43:25)
Continuity mistake: When Daniel grabs Nat's jacket he holds it right at the corner. When we see Daniel next, still frozen and his arm still up in the air, a biggish piece of the jacket is sticking out of his fist. (00:29:20)
Revealing mistake: When Daniel belly-lands his plane the rotors get totally bent. When the plane bounces back the rotors happily rotate again, revealing their rubbery consistency. (00:03:15)
Continuity mistake: Before Claire bandages Daniel's hand she buttons up her blouse. However, when she is sits down the blouse is open again. (00:44:40)
Chosen answer: Harry Findlay only discovered the ageing would irreversible after Daniel had been frozen; don't forget this was the first time he'd tried it on a human. Plus he only ever intended to freeze Daniel for a year, so this may not have been the main focus of the experiment anyway.