The Fourth Dimension
The Doctors remarks about his appearance as he looks into the mirror in Rose's flat, suggest his regeneration was a very recent one. However, this is the first and only time in which the circumstances of the Doctor's regeneration at the start of a series remain unexplained.
This is only the second time in which the Doctor regenerates without a companion, the first being Jon Pertwee's debut as the Third Doctor in Spearhead from Space (1970).
If you look closely at the photographs in Clive's shed you may notice that the Ninth Doctor is seen present at The Kennedy assassination, Krakatoa and Southampton on the eve of the Titanic voyage.
The coat stand seen in the TARDIS is the same style as the one featured in the original series.
Monsters For Dummies
Although not named in the episode, the plastic mannequins are correctly identified as Autons in the credits. They were created by Robert Holmes and featured in the adventures Spearhead From Space (1970) and Terror Of The Autons (1971).
This is the first episode in which the Doctor mentions the Time War, a running thread in the new series. If you're waiting to see what happened during it on screen, don't hold your breath! It's likely to remain a bit of a mystery.
This episode also sees the first reference to The Shadow Proclamation; we're left hanging about the meaning of who or what that might be until the The Stolen Earth (2008).
Word To The Wise
The search engine featured in the episode (wise.net) was created specifically for television and film use.
Who's In Control?
The force controlling the Autons, The Nestene Consciousness made its first appearance in the series in the story Spearhead from Space (1970).