Early in the film, it's said that there is a communications lag with Earth of just a couple seconds. Then it's said that they are only 30,000 miles from one character's favorite club/restaurant. Being only 30,000 miles from Earth would result in only a fraction-of-a-second radio delay.
Starting at 19:46,
When Dr Ryan is preparing a meal, (by the woman of course, this is a1950s movie), the contents of the shelves are quite different between the long shots and closeups. Also, Dr Ryans collar is different in these shots.
Irish claims the creature is single-celled like an amoeba, but it clearly has an eye, which would indicate something more complex.
Early in the film, it's said that there is a communications lag with Earth of just a couple seconds, adding "just wait until it's a couple hours!" But at their greatest separation, the radio lag between Earth and Mars would only be about 22 minutes.
When leaving the ship, the crew's space helmets lack protective glass.
At 9:04 two 'Radiation Monitors' in full radiation suit regalia climb aboard a fire truck for a ride to the returning spacecraft.
Driving right up to the spacecraft, the driver is is ordinary firefighter uniform, completely unprotected from any radiation.
After landing, O'Bannion cleans and readies a Colt M1911A1 automatic pistol. When he removes the magazine and checks it, it is empty and he doesn't load it. He inserts an empty magazine into the pistol so it is not ready to use for defense.
Earth has the advanced technology to send astronauts on a round-trip mission to Mars that takes mere days and sonic weapons that can crystallize organic substances in seconds, yet the astronauts have no type of vehicles available for exploration other than an inflatable emergency raft.
After chopping at one of the legs of the giant creature, Iris runs to hide behind some rocks along with Tom. When she reaches down to steady herself on a boulder, the boulder rocks back and forth, obviously made out of styrofoam or some other similar light material.
Les Tremayne clearly states that have deliberately landed on the equatorial area of Mars because that area is most likely to have life. Later Jack Khruschen, clearly contradicting that geography, asks where the polar caps are.
We are left to assume that four trained scientists - one of whom comments that its leg-shaped "trees" are at least 40 feet high - fail to notice the rat-bat-spider-crab monster standing in the midst of an otherwise empty plain.
Although Dr. Iris Ryan saw something outside the portal, all four leave the ship and go off to explore, leaving the ship open to anyone or any thing that may want to enter it. They should have left a guard or physically closed the entry so only they could enter the ship.
The CWO only keeps watch out one side of the ship. Anything approaching could come from the other direction and not be seen. He should have been moving been both portholes to observe in both directions.
Colonel O'Bannion has terrible gun safety manners for a career officer. He twirled the pistol around his finger inside the ship after cleaning and checking it. He has it out when they get outside the ship and keeps pointing at the other crew. He keeps his finger on the trigger the entire time, especially when pointing at the others.