Revealing mistake: In the catacombs of the library, Indy and Elsa are waist deep in petroleum. Indy has a torch, and if you look carefully, you will see burning pieces of the torch fall and hit the petroleum. Wouldn't this start a fire as Kazim later on sets the cavern alight with a single match?
Plot hole: When Indy is stepping on the letters at the end, trying to spell out God's name, he steps on J, incorrectly, causing it to collapse. When he falls through, however, he grabs onto another letter so as not to fall down. The letters he grabs onto and pulls himself up are an L and a Y, which are not in the word Iehova, so should have collapsed too.
Revealing mistake: When Indy has just climbed the stairs in the library and is leaning over the rail to look at the X below, directly behind him is one of the worst props I've ever seen - a flat fake book case.
Plot hole: At one point, Indy rolls off of the side of a tank, and somehow gets a strap around one of the guns pointing out from the sides. The end of the barrel has already been blown open by the rock he shoved in earlier. How did the strap get around that big cluster of metal, and then back again so he could climb back on the tank?
Continuity mistake: When Indy and gang are racing the Nazis to the canyon of the Crescent Moon, Indy looks at the Nazi convoy with binoculars. Close-ups of Indy show the sun is clearly behind him, and the binoculars are in his shadow. But then a glare from the lens alerts the Nazis to their presence.
Continuity mistake: When the tank goes over the cliff, the turret detaches upon impact. But in a subsequent shot, the tank is shown rolling over with the turret still attached.
Factual error: In this film, and in Raiders of the Lost Ark, the German vehicles are clearly marked with the DAK (Deutsch Afrika Korp) symbol (a swastika over a palm tree.) The DAK and its symbol were not created until 1941 when Hitler tried to rescue his Italian allies in North Africa.
Audio problem: When Indy confronts the butler at the castle, we hear the butler say, "...I am Mickey Mouse." But his lips say something else. He actually said "I am Jesse Owens". It was changed because they thought a lot of the audience wouldn't know who Jesse Owens (the black athlete who won at the Berlin Olympics) was.
Revealing mistake: During the "What happens at 11 o'clock?" joke, Jr. counts down ("12, 11, 10!" or something like that) with his hand, matte lines surround his hand to the point where it almost dissappears.
Continuity mistake: While Indy and Marcus are in the apartment in Venice, after Marcus says, "He knew everything, except the name of the city", he slams the diary shut. Then it's shown open, and he closes it a second time. When Indy takes it, it's once again open.
Continuity mistake: At one point Indiana's father blows the tail of the plane in which they were flying to pieces in an attempt to shoot at the Germans. This is obviously in a close-up studio shot. The next moment the plane is shown flying in the distance with its tail still intact.
Revealing mistake: A very obvious dummy replaces the Nazi when the tank hits the bottom of the cliff.
Other mistake: When they go under the coffin you see the flame of the torch in the background. How could the flame go under the petroleum with them without either setting light to the petroleum or being extinguished itself?
Other mistake: When Indy is breaking through the wall in the catacombs, and he uses his shoulder as a battering ram. You can see his head actually bounce off a piece of the rock real hard as he is going through the wall. If the rock was real, I guess Indy would have a lot to cry about that night.
Revealing mistake: Indy and Henry go through a tunnel to avoid the Nazi planes, but one flies into the tunnel anyway. When it goes into the tunnel, it's covered with matte lines, and it's the wrong color.
Factual error: When Indy and his father are being chased by the German soldiers on motorbikes they can be easily identified as modern lightweight Japanese trailbikes, not the big heavy bikes the German army used.
Factual error: German Fighters shown in the film are in fact Pilatus P-2 (Swiss-made aircraft built after World War II). The appropriate fighter of the period would be the Messerschmitt 109.
Other mistake: Just a small detail. Watch the tank roll over the hill with the German officer holding onto the top. When the tank hits the ground, the turret pops off. The German soldier (the prop dummy) maintains its grasp on the turret and is pulled off with it. The sheer force of the crash would have easily blown a human body off the tank.