Plot hole: Had one or more locomotives coupled onto the real runaway's front engine, or even just been pushed by it, anyone aboard the "rescue" engine could have just walked to the unoccupied ones and shut them down - no copters or fireballs required.
Plot hole: When Astrid gets on Toothless for the first time, Toothless takes off uncontrollably and tries to scare her. Hiccup seems to have no control over him at this time. How is that so if with the new tail fin, Toothless cannot fly without Hiccup's precise control of the tail fin? That whole sequence would have fallen apart. This mistake was even admitted to on the DVD commentary. (00:53:35)
Plot hole: When Claire is getting interviewed at the FBI building, there's pics of inside the bank during the robbery, even though the security tapes were destroyed in the microwave.
Plot hole: Modern diabetes management will tell a patient immediately if their glucose levels are out of the ordinary. Results are not monitored and delivered to a county jail by an outside lab. If a diabetic is sick enough, they would have obvious physical indications. The entire escape plan hinges upon these fallacies.
Plot hole: When Andromeda and Perseus wake up on the beach, Andromeda tells Perseus that Argos needs a new leader/king. The problem with this is there is nothing onscreen to show that she even knew her father the King had died. She was hanging by her arms facing the Kraken and she couldn't turn around. By the time her father died, she was already falling into the sea, so again, she shouldn't even know her father has died.
Plot hole: The water-borne biological weapon makes every individual a crazy murderer, right? Near the beginning a man burns his house with his wife and child inside. So then why do the three hunters not try to kill each other or the crazy wife in the nursery not try to kill her son?
Plot hole: In one of the last scenes when the scribe is putting the newly published bible on the shelf you can see next to it a big green book with the word Tanach written on it. That is actually a translated bible with the Hebrew and English, including the five books of Moses and psalms plus much more. He had the Bible the whole time. (01:47:50)
Suggested correction: From the internet movie database... The Hebrew Bible, or The Bible or "the Chumash" in Hebrew, is already in the library. The Christian "Old Testament" is the Chumash with some variations (reorder of books and reorder of the 10 commandments, depending on religious denomination). The New King James Version is an Old Testament with the Christian Gospels added at the end, some of which the main character, Eli, quotes. These two books would be considered separate and unique in a library.
Suggested correction: Not necessarily. Some engines may not have a rear cab access (like Frank/Will's engine had). And even if the rescue engine did have a rear cab access 777's engine only had a side access stair which at the speed it was going is more difficult to climb over from the engine in front of it.
Actually 777's catwalk goes across the front, from side stair to side stair, but someone would have to leap over a rail or a chain to get onto it from the other engine. Why would there be stairs on the right side unless there was a catwalk to get to the door on the left side?