The story turns on the idea that the earwig eating through the villain's brain was excruciating; the fact is that the brain has no nerve endings in itself. Neurosurgeons frequently operate on patients while awake in order to verify the correct location of an electrical stimulus.
The earwig is so named because people believe it behaves as depicted. However, this belief is completely untrue and has absolutely no basis in reality.
When Burke and Prof Putman (+ daughter) are at dinner, the coloring changes to a red-hue several times. This continues when Burke/Cottrell talk after the driving incident. However, this may be planned as the same effect is used in the final moments. As such, this is not considered a Goof.
Although in the original shooting script John Warwick personally heard Robinson telling Macy of the conspiracy and the assassination attempt going wrong, it doesn't happen in the final production and there is no explanation as to why John, Rhonda and Macy know of the contract on John's life that Steven placed.