Continuity mistake: Near the end, when Martha asks the Daleks what's going on and one of them explains that they are planning to evolve to live outside their shells, the Doctor changes position between shots while he's shown listening to this, standing behind Frank and Laszlo. (00:44:30)
Plot hole: The guy working for the Daleks offers the homeless men in Hooverville a dollar a day to go into the sewer because the Daleks need more people. Most of the people refused and one called it slave wages. If they were not getting paid until they came back, and since the Daleks were planning on experimenting on them, the people weren't going to come back; why not offer them a large amount of money big enough to entice them but small enough not to be suspicious?