Theory:Doctor Who television discontinuity and plot holes/The Underwater Menace


 * Why are some of the Fish People more "fishy" than others? On some you can see they have scales and fins, but on others, they look like humans with goggles on!
 * Stages of mutation/chang'e? Also, as their adaptation is a surgical procedure, there is no reason they should all be fitted with exactly the same set of implants, particularly since some of them (the less adapted ones) are seen in the marketplace. Quite possibly they are given different configurations of implants to carry out differently allotted tasks, some requiring greater amphibiousness than others.


 * When Zaroff fires his pistol (an ordinary, non-futuristic 9mm) at the end of episode three, he quite clearly does not: there is a sound effect, but no smoke, recoil, or discharged cartridge.
 * Production errors aren't plot discontinuities, any more than the fact that his 9mm is made up of scanlines on a cathode ray tube rather than 3-dimensional metal is.