Visible crew/equipment: During the campfire scene a Morlock attacks Weena, and drags her off. If you look at the top of the frame, as the Morlock drags her away, the stunt man's head can be seen, as he forgot to wear the head part of the costume.
Visible crew/equipment: The string holding up the "Fire Monster" to make it appear like it's standing upright is seen in a couple of shots.
Visible crew/equipment: When Colonel Martin stops to ask the sergeant what room Major Allison is in, the reflection of one of the cameramen moving around can be seen on the door's glass window.