Revealing mistake: At the end a shadow appears on the cliff under Indy's shoe when he steps to the edge. This would not have happened if a solid but camouflaged bridge were there. (01:47:30)
Continuity mistake: When we first see the knight guarding the Grail, his cloak is tied off with a braided rope, which hangs down on his right side. It stays this way until he says "You have chosen wisely," where the rope has somehow shifted to his left side. The rope goes back to normal when the knight waves goodbye at the end of the movie. (01:49:10 - 01:54:05)
Revealing mistake: The candles that adorn the wall in the Grail room do not appear to have a strong enough flame to put out the light they do that shines on the wall. In fact, it looks like there are electrical lamps just behind the candle. (01:49:20)
Visible crew/equipment: After Elsa gives Donavan the false Grail, he turns and you can see the reflection of the camera lens in the cup. (01:51:45)
Revealing mistake: When Donovan takes a drink from the false grail, he turns toward the camera and you can see the screw holding the base to the stem of the cup. (01:52:15)
Continuity mistake: In the temple in the Canyon of the Crescent Moon: After Harrison Ford cures Sean Connery by pouring water from the grail over him, Sean stands up with the grail in his hand. In the next shot, however, Alison Doody picks the grail up off the floor. (01:55:50)
Revealing mistake: Just as Elsa leaps from one side of the precipice to the other as the Temple collapses, a rock rolls from right to left and hits her right in the head before bouncing off. (01:56:35)
Continuity mistake: When Indy is trying to hold Elsa and keep her from falling and she's trying to reach the Grail, you can see her hand coming out of her glove. In the first shot of her hand coming out, it comes almost all the way out. In the next two shots, her hand is about halfway out, then it slips out and she falls. (01:57:00)
Visible crew/equipment: When Indy tries to reach the Grail his father convinces him to "Let it go" and Henry pulls his son to safety, then in the next wide shot of Indy, Henry, Sallah, and Marcus, we can see a crew member wearing a short sleeved, white shirt and blue pants at the right side of the screen, just before it cuts to Henry's closeup. This crew member can be seen again after the closeup of the knight. (01:57:45)
Continuity mistake: When Indy is stepping on the letters, he steps on the "O" and knocks the "P" loose. In the next shot, the "P" is intact.
Visible crew/equipment: When the lead bandit opens the magic cart door to find young Indy running away on the track, a crew member wearing a white shirt can be seen reflected on the door.
Continuity mistake: When Indy comes face-to-face with Hitler he hands over Henry's diary with its black elastic around the back cover, but in the closeup as the signature is being signed the elastic is around the front cover, then it's around the back cover again when Indy takes the diary back.
Continuity mistake: When Indy and Vogel are fighting atop the tank we see the soles of Vogel's boots and there is a red hexagon dot under each heel, but while Indy is hanging off the tank's side mount gun the soles of Vogel's boots are different.
Other mistake: While Indy and Henry are aboard the zeppelin Indy tosses Vogel out the lounge window, and when Vogel shouts up to the departing airship, in the next exterior shot we see the zeppelin airborne against a scenic view. Later, when Indy realises the zeppelin is turning around it cuts to another exterior shot of the airship, and the scenic view is identical to the earlier shot, only it's been flipped. The images of the zeppelin facing two different directions were composited onto the same scenic background.
Continuity mistake: In the temple in the Canyon of the Crescent Moon, Indiana Jones rushes to his father's aid with the Holy Grail filled with water. He is shown pouring every last drop onto his father's wound by turning the Grail upside down, yet another camera angle shows his father clutching the grail to his chest, and there's still a bit of water in it.
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 disappears.
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 is being chased by the tank there is a type 82 Kübelwagen - they weren't produced until 1940 and the movie is set in 1938.
Continuity mistake: In the motorcycle chase scene after the escape from Brunwald castle, Indy's hair is noticeably longer than it was in the castle scenes. It returns to the shorter length when they stop at the crossroads.
Continuity mistake: In the beginning of the boat chase two bullets hit the windscreen of Indy's boat. In the next shot the location of the holes has changed.
Answer: The implication is that disaster would follow them outside of the cave as well. It wouldn't make much sense if you could simply outrun the disaster.
BaconIsMyBFF
"Followed by disaster" is a kind of curse, a thing not common in Christianity. It doesn't make much sense anyhow. A seal is just a dot - OK, so let's at least grant that the seal represents a circle that the grail has to stay in. Who decided where those borders are? The grail was taken there during the first crusade. That was closer to 1938 than it was to 33 AD. The three knights could move the grail about then. Why not afterwards? The knights could have built the traps. But the borders could only have been set by god, in an unusually late and completely atypical miracle.
Spiny Norman
There are several examples of curses in the Christian Bible: Lot's wife is turned into a pillar of salt for looking back at Sodom, the plagues visited upon Egypt, Adam and Eve are cursed for eating fruit from the tree of knowledge, etc. The knights did not move the grail around after finding it, they stayed in the temple for 150 years and then two left leaving the third behind. The great seal and it's restriction was already in place when the knights got there.
BaconIsMyBFF
Where in the movie is that stated? I interpreted the knight's story as them having made that place. Looks like it isn't actually specified. But if God made it, then I submit that he would have used Greek, not Latin, for the stepping stones. (All of those curses are from the old testament. The book where god kills firstborn children as long as they're Egyptian. Grail is by definition new testament where you turn the other cheek. There simply are no curses in the gospel, that's just not how Jesus rolled).
Spiny Norman
The tests were made by the knights, but the seal had God's power in it. Just like the cup.
lionhead
It's still a bit dodgy. What if you take a shovel and dig yourself a back door? Basically this film really excels at stuff that makes no sense but helps the storytelling, or to be precise, creates dramatic effects.
Spiny Norman
Every fictional story is like that in some way. That's why it's called fictional. It's just a story.
lionhead
Not a particularly convincing argument, "stuff happens for no reason all the time", if I may say so. Why is this website even here then? The fact is that some stories are more coherent than others. (♫ "In olden days, a hole in the plot, would seem to matter, quite a lot. Now heaven knows, anything goes..." ♫);).
Spiny Norman
It's the difference in what story they want told. Is it a fairy tale or based on actual events? A huge difference in plausibility between the two. The site is there to look at mistakes, not how believable the story is.
lionhead
It is not set in another universe so plausibility isn't somehow suspended. Maybe take a look at the categories recognised by this website. Plot holes, factual errors, even stupidity. (They? Who are they?).
Spiny Norman
It is set in a fictional universe because it's not a true story. With "they" I mean the writers/director. Mistakes in a plot (plot holes) have nothing to do with how believable the story is. As long as it's plausible, it's not a mistake.
lionhead
Pretty sure it's the same universe, just with some added characters/events. What about the total lack of spaceships or orcs or talking animals for example? The seal business is not a mistake YET, but it's very dodgy because no-one knows how it works or why. Like all Indys "trapped" secret places, it's (among other things) unclear who resets the traps for the next visitor. We can't brush it ALL off as "the hand of god" every time.
Spiny Norman
Huge amounts of stuff in films isn't exhaustively explained. Doesn't mean there isn't an explanation that's perfectly believable. There's zero evidence either way to say how "followed by disaster" would manifest, and just because there's not a thorough explanation doesn't mean that it's "dodgy", and it's not worth bickering about either, because there's no concrete answer either way.
Jon Sandys ★
OK but I would like to note that not everyone who offers creative explanations has recently seen the movie; some people just invent their own. E.g. "followed by disaster" is not an actual explanation from the movie, it was just one of the suggestions made here and only here. Or the ones on my own question below. All I'm saying is, it's very hard to tell what the "rules" / "logic" of this place are supposed to be, so I understand what the OP was driving at.
Spiny Norman