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)
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)
Visible crew/equipment: Martin Brundle (in fly form) manages to kill a guard by spewing acid vomit all over him. Right after this happens he roars and you can see what looks like a colander (probably used to increase the spread of the vomit) in his mouth.
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.
Chosen answer: Obviously, he was kept alive so he could be studied, which was a nasty twist on the fact that he kept the dog alive, and suffering, for so long. As far as the food, there is no way to know what it was. Probably some kind of bland mush.
wizard_of_gore