While looking at the beast from the diving bell, Professor Elon refers to it as "paleolithic survival." The Paleolithic period goes back only as far as 2.6 million years, but the professor also claimed that the beast would be at least 100 million years old.
When Prof Nesbitt is being interviewed in the hospital shortly after the start of the movie, he is being told that sea monsters do not exist and the interviewer mentions Loch Lomond as an example. He obviously means the Loch Ness monster. Given that, he is further erroneous in stating that it had never been photographed, as one of the most famous photos of "Nessie" was taken in the 1930s.
Just after the beast enters New York City, a policeman approaches him on foot firing a pistol at the monster. The beast then picks up the policeman and proceeds to eat him. Several scenes later, a group of four policemen is shown approaching the beast with rifles. The officer who had just moments before served as "lunch" for the beast is clearly one of the four officers.
As the policeman fires a pistol at the monster, the beast picks up the policeman and proceeds to eat him. As the officer begins firing, he is next to a car and the passenger side door is open. When he is bitten and lifted off the ground the same passenger side door is now closed.
The diving bell entry it rife with problems. When it starts, heavy anchor chain is shown reeling out but the next show shows a multiple block and tackle arrangement with ropes in use from a boom. Then the anchor chain is shown again. As it enters the water, there is no boom rope at all. After it is in the water there is rope again but far too long for rope to be used. On the surface, and in the port hole shots, lots of bubbles are shown but none are coming from the diving bell.
When the fishing vessel "Fortune" is attacked by the Beast, it is shown moving from right to left. In the wheelhouse, Jacob looks to the left, which would be port, and reacts in horror as he sees the Beast rise up out of the water. The Beast then pounces right away, crushing the wheelhouse roof down, then the shot switches to the exterior. The ship is still moving right to left, but the Beast is shown attacking from the starboard side of the ship, when it should have been attacking off the port, where Jacob had just seen it.
When Prof. Nesbitt is in Lee Hunter's apartment, going over sketches of different dinosaurs, Lee hands the Prof a sketch, and when she does we get a quick glance of it as he takes it from her. When the camera then shows what sketch he is holding and pointing to, it is obviously not the sketch that Lee had just handed him a moment before.
The monster is reported to be in "Manhattan Beach", and when the authorities arrive there they discover it in a big amusement park. This park is actually a replica of that at Coney Island, which is actually several miles from Manhattan Beach in Brooklyn; there's never been an amusement park such as this in Manhattan Beach.
When the four men are traveling aboard the half-track near the beginning of the movie, the far distant mountains in the background are moving past very rapidly. For that to occur, at that rate, the half-track would need to be moving at 1,000mph or greater. It would have been far more realistic if the background mountains had remained completely stationary while the half-track was simulating movement forward.
The aircraft shown in the beginning approaching the bomb drop is a Douglas DC-3S. The speed announced by the person tracking the plane's progress is 360 mph. The top speed of the DC3S was 250 mph. It also is a cargo plane and has neither a bomb rack nor anywhere near the range quoted in the movie.
As the diving bell is shown moving up and down in the depths of the ocean, it's moving far too fast. The rate of movement is all out of proportion to size of the bell and the supposed depths involved. Things raised and lowered in the ocean by cable can move at the speeds shown in the film; things are out of scale.
Shortly after the beast comes ashore in New York, he is shown emerging onto a street from a side street, and pausing. Behind him are a number of cars and pedestrians who continue to drive or walk casually, which they would certainly not be doing if a huge prehistoric monster had just appeared less than a block away.
In the shot of people fleeing down the subway steps to escape the beast, the monster is shown approaching from behind, but the building next to the steps collapses and rains debris down on the pedestrians before the monster has gotten close enough to destroy the building.
At the end of the underwater struggle between the octopus and the shark, a segment of the fight is run and then played in reverse to stretch the scene out. You can see the shark twist, pause, and then reverse its movements.
(at around 15 mins) In the scene in which the scared pedestrians are fleeing down the subway steps with the Beast close behind them, one man, in a dark overcoat and lighter hat with dark band, telegraphs the collapse of the subway wall and raining debris by raising his arm head high to protect himself *before* the wall collapses.
During the diving bell sequence, there is a fight between an octopus and a shark. Early on, as the octopus tries to get away, it can be seen that it is using the glass wall of its aquarium to move itself.
The fact that the roller coaster is in Long Beach, Cal, not New York (already noted under Trivia) is revealed by the scene in which the two men climb into the cars. They didn't cover up the sign which says "Cyclone Racer." New York's coaster is just called "Cyclone." And in one of the outdoor shots you can see the "Jackrabbit Racer" which is also in Long Beach.