Not really hidden but a mistake...In the prom scene where Bill Allen (Cru Jones) and Lori Laughlin (Christian) "bike dance" you can see the obvious stunt doubles, but better yet on a closeup of Lori Lauglin performing a trick, her back tire gets in the picture and it is not even moving.

In the first scene at the La Motta apartment, Jake (De Niro) asks his brother Joe (Joe Pesci) to hit him as hard as he can. After hitting Jake a couple of times, we see blood has spattered on Jake's face. Then the camera cuts briefly back to Joe. When it cuts back to Jake, the blood is gone.

In the Cairo street scene where Indy encounters the Black Turban wearing Arab with the extra large sword-there was a very large action scene planned. Harrison Ford was very ill that day of the shoot with diareeha and wasn't up to shooting that day. Ford suggested to Speilberg "Why don't I just shoot the guy with the sword". Ford felt that he could stand to shoot that scene,although he was ill, and the production would not fall behinde schedule. It would take a 1/3 of the time to film and Ford to return to his trailer to rest. The crew laughed at the suggestion and Speilberg went for it. An improv' scene that, without a doubt, is one of the most memoriable scenes in the Jones trilogy. This also illustrates Speilberg's philosophy-always be open to suggestions on the set.

When he fell in the snake pit you could see a reflection of the Cobra off the glass separateing them.

The scene where Indy escapes from being trapped underground, after locating the Ark the first time, you see him pushing a large stone out of a wall to get outside. But before you see the stone fall out, keep watching its shadow as it drops on the ground...it bounces! An object such as this should be too heavy to bounce.

When Indy is threatening the Nazis with a bazooka, the evil guy in a white suit who argues with Indy accidentally eats a fly who lands near his lip and crawls into his mouth. Eeeeew!

The main bad guy is talking to Indiana Jones as Indy is up on a cliff about to be shot and the bad Nazi has Mariam, Indy's girl. As the bad man is speaking, a fly lands on his lip and goes into his mouth. He keeps talking like normal, but you can picture by his expression he knows what just happened. The editors even went in later and if you turn up the volume you can hear the buzzing fly sound as it goes onto his mouth.

Look closely at the end of the film when Harrison Ford is running out of the bunker on the planet. He screams for everyone to get out of the way and you can see his reflection in the plexiglass that the crew setup to protect him from the explosion.

In the non-mastered version of the film when Jabba pulls the slave-dancer girl into the Rancor Pit, her boob pops out of the costume. How embarassing!

Blooper or comment on the car?

Not so much something that is hidden but a editing mistake. When Rocky is on the beach training for his rematch with Clubber Lang (Mr. T), he starts having flashbacks to the first fight, which he lost. However, one of these flashbacks shows a clip from the second fight, which has yet to occur in movie time and which Rocky goes on to win.At the end of the first round of their second fight, you could still see Clubber Lang (Mr.T) bob his head up a couple more times as if he is getting hit by more punches, although Rocky has already stopped punching.During the second fight between Clubber and Rocky, the words "Heavyweight Champ" on the back of Clubber's cornermen are backwards as if in a mirror. also the word "Clubber" on his tights is backwards, almost as if he came out of the same corner as Rocky then they just flipped the screen to make it appear as the opposite corner, they forgot about the words though.

As we all know Sly Stallone is short, actually shorter than his movie wife. So when having face to face you never see the two of them in full profile. When the two of them are shown in full view(while Rocky is training in Russia)a body double is obviously used! Just look at the outline of Rocky's leather coat, it goes from a V shape with Sly to a fat guy standing with Talia Shire.