When the ship is sinking and the water crashes through the big glass dome above the grand staircase, in the first take the water actually broke the staircase off the wall and crashing into the actors who were in the scene. See more...
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Continuity: About half an hour in when the rear of Titanic is shown, look at the very rear of the ship and you will see a red sign (near the triple screws) to the right of an over-hanging light. Shortly afterwards when Rose approaches the rear of the ship to jump off, the sign has now moved to the other side of the light.