Goofs

Frank adds a powder to the vial to color Geoffrey's invisible blood. When he adds the blood in close up, the vial is empty.

In The Invisible Man (1933), the main ingredient for the invisibility formula was "monocaine"; in this film it's called "duocaine".

Geoffrey has dinner with Frank and Helen to celebrate his success. During the meal, Geoffrey drinks a glass of champagne. The champagne disappears when Geoffrey drinks it. It should have been visible as it went down his throat.

Sorry to mention this but the whole "Invisible Man" series makes the same mistake. To be invisible his body could not reflect or refract light. If his eyes didn't refract light, he would be blind.

In The Invisible Man (1933) the invisibility drug had to be taken repeatedly over several weeks to be effective. Here (and in the later film Invisible Agent (1942)) it works instantly after only one injection but it has been nine years since Jack Griffin's death and all the while his brother Frank has been working on trying to improve the formula.

In many places, the matte process used in the production is visible.

When the mining car dumped Mr. Cobb out, it was packed to the rim with heavy rocks but as he fell, only a large trail of dust came out behind him.

The wires holding the gun are clearly visible.

About 45 minutes into the movie, soon after the Inspector arrives in the open car, there is a scene change to the laboratory. Very soon after the scene change you can hear a crew member (or someone) cough.

(at around 1 min) As the doctor prepares to enter a small room where lab animals are kept, through the window of the door can be seen the moving shadow of a man.

Like the original, this film is set in England, but at one point the condemned hero's lover is hoping for him to get a reprieve from "the governor." This is a staple of American films about executions, but there are no state officials called "governor" who could pardon a condemned man in Great Britain.

Geoffrey was shot towards the end of the film. Assuming the bullet entered the body, it should have been visible. Furthermore, his friend says he can't see to operate, but all he had to do was spray or paint him with some makeup. Putting makeup or some such substance on Geoffrey's skin would enable the doctor to see the skin, but he could hardly do the same on the internal organs he was to operate on.

Geoffrey Radcliffe had been invisible for several days through the course of the film. As such, it would have been impossible to see his reflection in a mirror and therefore he couldn't groom himself. Yet when he becomes visible in the final scene, he is perfectly clean-shaven and his hair impeccably combed.

Geoffrey "The Invisible Man" was eating and cleaning his mouth with a tissue and was planning to drink a toast while he remained veiled, when he was having supper with Dr. Frank and Helen.