In the scene in the library in Venice when Indy, Dr. Elsa Schnieder and Marcus Brody. Indy finds that X marks the spot. The next scene is Indy breaking through the floor. Notice that the X has disappeared. Whoops!
I just watched the DVD today, and actually noticed this, too. Even reviewed the whole scene again just to make sure. From the top of the staircase we can see a large "X" in dark (green?) floor tiles on a white tile background. The white tiles for a square, which is bordered by dark red tiles. When Indy is breaking the floor, it is a solid green square outlined by the red. No white, no "X". No matter what angle you view it at, the "X" is completely gone.
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The X HAS gone! Directly after the comical scene with the librarian who is confused by the loud stamping sounds, we cut back to our heroes to see a wide shot of Indy breaking the floor. The X has been replaced with a large, grey, blank floor. No X!
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The "X" is both there and is not there.
The original "X" first seen by Ford was placed there by the production team. If you look closely, you can notice the edges of the X glimmer. The glimmering likely indicates an adhesive used to attach the X to the floor.
In the scene where Ford is breaking the floor, the outline of the X is faintly visible. The X can only be scene because the adhesive used to attach the X to the floor left an outline.
Thus, this is indeed a blooper. The X was removed in the latter scene, and only the outline of the former X is visible.
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The X is NOT there. If you look just prior to where he climbs up the stairs, you can plainly make out not only the X but the different white/red/black colors on the tiles. Once he comes down and he's pounding on the floor with the metal thing, you can see from a wide angle that it's gone. Compare the size of the X and surrounding white area in the shots before he climbs to after and you can plainly see that it's missing.
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The X IS there. It can be seen when Indy is digging the floor up, although it is faint. Maybe you need to review your requirements for this slip-up because sharp eyes are something that you obviously don't possess.
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That's right. If they made it too obvious then there would be no challenge to finding the Grail. So you had to be at a different angle to see the big X. But if you look closely enough to the floor when they are there....you can make out the X.
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