Corrected entry: When Ace watches Kara approaching the lake, look closely, and you will see the power lines in the background of the (supposedly primitive) Cheetah Planet. The Cheetah people don't seem to have discovered electricity, so why the need for overhead power lines?
Corrected entry: How is it that The Master recognises the Doctor, despite never having seen him before in his seventh (Sylvester McCoy) regeneration/incarnation?
Correction: It's been stated that Time Lords are partially telepathic "at least with each other" (stated by Dr. 4 in The Deadly Assassain). The Master probably recognized the Doctor by this telepathy. Otherwise, in a society that uses regeneration, people would have a hard time recognizing each other.
Correction: The power lines are probably remnants left behind behind the people who tried to colonise the planet before finding themselves "bewitched" by it (just like the remnants of buildings that the Master shows the Doctor).