1)The first of this season's "double banking" episodes - this one focusing on the Doctor. It occurred to me while watching this last night, that it's probably only the third time I've watched, after the initial broadcast and when I first got the DVD set. It's not that I think it's a bad episode, it's more that it's so odd as a story. Basically a "one-set" story - in the commentary track, David Tennant says that this story only had about nine scenes, where an average story has about eighty - it's very claustrophobic. The Doctor is in an odd position here, we've never seen him so helpless. It's funny to think that this nameless creature came closer to taking him out than umpty numbers of Daleks. It's also interesting to see him in a situation where his usual ability to talk his way out of things fails him utterly.
2)I thought the woman playing Sky did a very good job in this. It must've been a bugger-and-a-half synching up with everyone like that.
3)The Professor was played by David (son of Patrick) Troughton, looking a tad different than he did in his "King Peladon" days.
4)"What could possibly go worng?" He should know better than to say that.
As I said above - it's weird. A good episode, but not one I could re-watch too often. In some ways, far scarier than any number of Moffat horror shows.
[Part of list of Doctor Who episodes here.]
Lesley Sharp was the featured actress here. She had worked with RTD before on his series "Bob and Rose" and his very interesting, but controversial, mini-series, "The Second Coming" co-starring with Christopher Eccleston as, you guessed it, the second coming of Christ. Jessica Hynes was also in "Bob and Rose".
This was a cracking little episode. As you say, scarier than some that 'tried' harder to be frightening.
The copying entity was another adaption of playground shenanigans into something more memorable, like how statue games became the weeping angels. The programme is deliberately speaking to its younger fans in their own language here, to good effect.
This is RTD challenging himself to write something that isn't as susceptible to the criticisms you lay at his door elsewhere. It is self-contained (no contrived links to the series arc), fairly logical within itself and doesn't bend itself out of shape to give the viewers big thrills and loads of story within the 45 min timeslot.
ABC Australia has been reshowing all the New Who these days on a nightly basis. They are at the End of Time now, but I might look to see if this episode is still on their iview service, to be viewed again.