Revealing mistake: When Beth is helping Martin out of Bartok's cocoon, you can see Martin wearing pants inside the cocoon. Surely he should be naked. (01:35:15)
Revealing mistake: In the scene where Martin Brundle has transformed into the fly he kills one of the guards by breaking his neck. After this he throws the body towards a door where another guard is standing - the body is a plastic dummy as it flies across the room with no effort at all and when the other guard behind the door checks the body you can see a plastic yellow face which is supposed to be the guard that was killed.
Revealing mistake: In a hallway scene, where the transformed Martin Brundle is throwing one of the scientists upstairs towards a guard, you can see the wires the scientist is hanging on. (01:23:05)
Chosen answer: They were studying the mutation. It was cruel to keep the animal alive, but they didn't care about that.
wizard_of_gore