Continuity mistake: The city railroad scenes were filmed in Spain, and many of the forest railroad scenes were filmed in Finland; in both of those countries, most of the railroad track is broad gauge (the rails are more than 5 feet apart). The plains and mountains railroad scenes were largely shot in Canada, where the rails are "standard gauge": 4' 8 & 1/2" apart. The rails can be seen to jump between far apart and closer together more than once as the movie progresses.
Continuity mistake: In the beginning of the film when Natalie Wood first gets in the limo, she is waving goodbye to her mother who is on the pavement. As the limo is driving away and Wood is leaning out the window waving, there is a lamp post behind her that is so close it looks like it might hit her. When the camera moves back to her mother you cannot see the lamp post.
Continuity mistake: In the scene where Rusty is trying to keep Dana and Valerie from seeing each other, it is supposed to be night time. But, when Rusty opens to curtains to usher Valerie out the door, you can see that the sky is much too light to be night time.