Revealing mistake: When the thug with the blade sticking out his back is standing still, there is some kind of squared device on his back under his clothes, presumably to retract the fake blade to end the sequence.
Audio problem: In Marion's bar, she uses a burning log to knock one of the goons out. As his face changes, you hear "ow!" then he moans as he falls over. However, his mouth doesn't match any of the sounds.
Continuity mistake: When Indy is shot in the arm in the car, there's no blood on the windscreen at first, but in the very next shot there is.
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: The amount of moss behind the idol increases between shots.
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.
Audio problem: While Indy tries to escape from the Well of Souls a stick in his mouth falls on Marion, who starts to cry very loudly; however, her mouth doesn't move an inch.
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 Marion's been thrown in the Well of Souls, a net and pair of sticks over the crate behind Belloq appear or disappear randomly between shots.
Continuity mistake: After the kids save Indy at the bar, he exits and there's a man on the right carrying a load on his shoulder. He appears and disappears randomly depending on the angle.
Continuity mistake: When Indy's crew is lifting the stone door to access the Well of Souls, big clouds of white smoke come out from every corner. A frame later, from a wider angle, they're gone.
Continuity mistake: About to grab the idol, Indy passes a stick over a pile of sand on the ground which has a leaf on the center. A frame later the leaf is on the left side.
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.