Doctor Who Season 3 Episode 10

Sally: (seeing The Doctor on-screen) Who is he?
Larry: An easter egg.
Sally: Excuse me?
Larry: Like a DVD extra, yeah? You know how on DVDs, they put extras, documentaries and stuff? Well, sometimes they put on hidden ones and they call them easter eggs. You have to go looking for them, follow a bunch of clues in the menu screen.
The Doctor: (on-screen) Complicated.
Larry: (pausing the DVD) Sorry. It's interesting, actually. He is on seventeen different DVDs. There are seventeen totally unrelated DVDs all with him on. Always hidden away, always a secret. Not even the publishers know how he got there. I've talked to the manufacturers, right, they don't even know. It's like he's a ghost DVD extra, just shows up where he's not supposed to be, but only on those. Those seventeen.
Sally: Well, what does he do?
Larry: Just sits there, making random remarks. It's like we're hearing half a conversation.