Corrected entry: The Bene Gesserit Reverend Mother arrives on Caladan to test Paul Atreidies with The Box and the Gom Jabbar, a test in which failure means death. His mother Jessica, also a Bene Gesserit, leaves the room. It seems that it isn't until she returns to the room, sees Paul alive and states 'My son lives', that she knows he has passed the test and is alive. When Arrakis is overtaken by the Harkonen, Paul and Jessica are banished to the desert. During this period Duke Leto dies and Jessica 'senses' it and becomes quite distraught. If Jessica, using her Bene Gesserit powers could sense Leto's death hundreds of miles away, why couldn't she sense whether Paul, who was only in the same building was alive or dead, but had to wait until she saw him?
Correction: Because a Reverend Mother was in the room with Paul - she could easily have been shielding the room with thought to ensure that no outside forces would interfere with the testing. According to the books, they could do that. That could easily explain why Jessica had no knowldege of the happenings in the room.
Corrected entry: When the Freemen put out several Thumpers before the big fight, take a look at them. Some are thumping down, others are backwards and thumping up.
Correction: Not really a mistake. It is mentioned that the thumpers are handmade by the Fremen. Different craftsmen use different styles.
Corrected entry: (TV version only). At the climax, Paul demonstrates his new powers by making it rain on Arrakis. This would kill all the sand worms as water is poisonous to them and destroy the spice (the worms are vital to its creation). Since Paul's fulfilling of the prophecy relies heavily on him being able to produce and regulate the spice supply, having it rain on the planet would effectively destroy his stranglehold and ruins his chances of doing so.
Correction: Yes, but who's to say that he made it rain ALL OVER the planet? It could've simply been a brief, localized shower (around the palace region) meant to demonstrate Paul's power and that he is, in fact, the Kwisatz Haderach of prophecy. As an interesting sidenote, the Fremen were storing water to "change the face of Arrakis"... Apparently they never intended to save the sandworms or the spice (originally) - they treasure the planet itself far more.