Veteran stunt man Tom Steele replaced James Arness in the fire scene. Steele wore an asbestos suit with a special fiberglass helmet with an oxygen supply underneath. He used a 100% oxygen supply which was highly combustible. It was pure luck he didn't burn his lungs whilst breathing in the mixture.
When Scotty mentions having attended the 1928 execution of Ruth Snyder and Judd Grey, another character asks him if he was able to get a picture of it. Scotty answers, "No, they didn't allow cameras, but one guy - " He is interrupted by the Thing's approach before he can finish the sentence. Scotty is referring to Chicago Tribune photographer Tom Howard, who smuggled a miniature camera into the execution chamber strapped to his ankle and was able to take a famous photograph of Snyder's final moments in the electric chair.
When producer Howard Hawks attempted to get insurance for the creature, five insurance companies turned him down because "The Thing" was to be frozen in a block of ice, hacked by axes, attacked by dogs, lit on fire, and electrocuted.
According to make up artist Lee Greenway, he took James Arness in his car to the home of producer Howard Hawks to show off the make up for the Thing. After months of frustration, Hawks told Greenway to put a Frankenstein (1931) type of head piece on Arness.
It is generally believed that Howard Hawks took over direction during production, and it has always been acknowledged by director Christian Nyby that Hawks was the guiding hand. However, in an interview James Arness said that while Hawks spent a lot of time on the set, it was Nyby who actually directed the picture, not Hawks.
Howard Hawks asked the US Air Force for assistance in making the film. He was refused because the top brass felt that such cooperation would compromise the U.S. government's official stance that UFOs didn't exist.
Scotty mentions being at the execution of Ruth Snyder and Judd Gray. This is a real case. The couple were tried for and convicted of the murder of Snyder's husband in 1927 and were executed in New York by the electric chair.
As opposed to that interview with James Arness, the film's Star, Kenneth Tobey has maintained in many interviews that it was indeed Hawks who directed the film. Tobey said that he had worked with Nyby after this film on many occasions and he was a fine director, but Hawks did call the shots on most of the film.
When they are all flying out to the crash site for the first time, they see where the aircraft has landed and discuss it. It touched down, skidded and then came to stop and melted through the ice. They show a long shot of the skid and where it finally stopped. If you slow motion the film or stop it, it reveals the following: At the beginning of the skid, the touchdown point, there is what looks like a guy in a hat knelt down by a machine of some sort. That could be the ice cutting machine that made the entire etching for the scene.
Originally, it was intended to make the creature a shape-changer as in the novel, but the limited budget forced the film makers to drop the idea. Early conceptual sketches depict a very plant-like looking creature with one of its limbs seemingly undergoing a transformation into a human hand.
Charles Lederer's original script featured a inhuman-looking creature looking almost exactly like the novel's creature in its original form (blue-skinned, with three red eyes, a sucker mouth and stringy hair), but the budget resulted in a simpler-looking alien again. Allegedly, test footage was shot featuring a creature with the earlier alien design, played by a one-legged man.
John Wayne was offered the lead in the TV series Gunsmoke, he recommended James Arness. In the first ever episode it is introduced by John Wayne who endorses Arness. James Arness suffered an injury while in the service and actually had a limp and found it difficult to film long scenes in the saddle.