Film Errors

In this week's Spectator the film review mentions a note being torn up in the film "The Bucket List" only for the same note to appear intact later.
It is a wonder that mistakes like this can occur what with all the attention to detail involved in film making.
The film "Roman Hoiliday" has a scene with the stars, Gregory Peck and Audrey Hepburn, in a square in Rome with a clock showing a certain time; seconds later in film time the clock shows a time hours different from that. Where was the continuity expert?
The craziest thing I have seen was in the local fleapit of a cinema I used to go to when I was a kid. A Hopalong Cassidy western was being shown. Back then the film was shown in three or four reels. Since the film didn't have much of a story, a lot of chasing villains and shooting, I wonder if many people noticed that the horseshoe they were looking for in reel number 3 had already been found in reel number 2.
Some projectionists there were then!
But it didn't seem to matter; the audience enjoyed the film, there was the big shoot-out at the end, the hero got his man and the young male lead got the young female lead.
Hopalong wasn't much interested in women. Nor was his side-kick, rough, beared old Gabby Hayes. The film always ended happily with Gabby saying something daft and Hopalong and the others laughing.
Including the horses.