Other mistake: In the opening scene Indiana is with horses and scouts. A few minutes later he is running for his life and in a few moments he's at a waiting plane. Why does he need scouts and horses for the cave is in walking distance from the plane and how did the scouts and horses get there?
Character mistake: Watch the extras playing the Cairo civilians walking around just before the big swordsman reveals himself to Indy. Several of them are just aimlessly walking back and forth as if they have no idea where to go.
Continuity mistake: The amount of dates change from shot to shot before they are poisoned.
Continuity mistake: At the market in Cairo just after one of the guys tries to kill Indy with a sword and misses, the shadow from the wall changes between shots.
Continuity mistake: When Indiana is fighting the bad guys at the market in Cairo, one of them kills another one with a sword instead of Indy - their position changes between shots.
Continuity mistake: Belloq grabs the idol from below its ear. When the angle changes he is holding it by the idol's temple.
Continuity mistake: When the guy at the start who betrayed Indy is shown stabbed by many spears, in the shot when Indy says "adios", he stays with him the entire shot. However, in the next shot, he's far away from him.
Continuity mistake: When seen from the outside the entry hole to the Map Room is quite vertical. The angle is different when seen from the inside. Further, the hole is so vertical that the sun wouldn't be high enough to shin through the hole at 9 am.
Continuity mistake: After the door to the Well of Souls is opened, Indy and Sallah take a sneak peek at the inside, immediately after, from a new angle, Indy sneaks in again.
Continuity mistake: The position of the dead monkey and the date next to him changes between the first and second angle.
Continuity mistake: The morning after Indy makes out with Marion, when he goes to check why the boat engines have stopped, the position of her hands, the wrinkles on the blanket and the dress behind the bed change positions between angles.
Continuity mistake: Indy walks to the hill where the ark is, holding a shovel that keeps facing different directions depending on the camera angle. Also, Indy holds it either by its black metal part or by the wooden stick. This all changes back and forth.
Continuity mistake: In the map room, Indy places his brush facing a 9 o'clock direction. A frame later it faces a 6 o'clock.
Continuity mistake: In the map room, Indy brushes the sand off of a stone, leaving a clean horizontal trail. A frame later, in the close-up, the upper left part above the trail is suddenly clean.
Continuity mistake: When Belloq traps Indy in the Well of Souls the sky keeps swapping between a dim yellow dawn sky, and a brilliant morning blue sky.
Continuity mistake: While Indy descends the Well of Souls the glowing logs underneath keep changing positions.
Continuity mistake: In the bar, the Nazi plays with the fireplace and threatens Marion, who takes a cigarette to her lips. A frame later, her hand is in a totally different position.
Continuity mistake: After the guy with the patch and the monkey greets the Nazis, Marion and Indy are seen walking through town, passing by an arched door. A frame later, from a different angle, they are passing by again and the amount of people around has increased.
Continuity mistake: Arnold holds a hot stick of metal to Marion's face in her bar, threatening her. In the opposite angle, the metal is nowhere to be seen when it should be right next to her face. Cut back to the other angle and we see it again.
Continuity mistake: In front of the idol, Indy shows Satipo the trap on the floor. Satipo's head position is different in all 3 shots in barely 2 seconds: First he's looking downwards, then straight, then his head is turned sideways, and then back to straight. (00:08:20)
Answer: The scene you describe was indeed filmed. It was cut out of the US release of the film although I cannot speak for the Australian version. The scene also appears in the Marvel Comics adaptation. http://www.theraider.net/films/raiders/deleted_scenes.php has a list of this and the other deleted scenes.
Phil C.