Goofs

Much is made over the fact that Dr. Melton, the murder victim, was left-handed. Yet, earlier, he was seen doing various things, such as taking notes, opening a door, and turning on the fatal light switch, all with his right hand.

The mounted gargoyle head in the scientist's lab is able to swivel, following Birmingham's movements due to photo-electric sensor, yet when knocked over in gunfire, it's shown to be constructed on a simple wooden mount (a pole with a circular base) with no wiring involved whatsoever.

The electromagnet used to fire the gun, did not affect any other metal objects in the room.

The prop for the electromagnet was a toilet float ball attached to a lamp.

It's 1944 and the housekeeper is dressed as if it's the late 19th or early 20th Century.

Although set in Washington D.C., in the first exterior shot when Charlie Chan leaves the office building you see the California state flag outside.

While Charlie Chan is riding in a taxicab to the murdered doctor's house in "Washington, D.C.", several exterior shots show the taxi driving through a neighborhood full of houses with red tile roofs and palm trees in the front yards... similar to that of West Los Angeles, California.