So far, Martha is brilliant. She's clever and can work things out without the Doctor telling her, so she can be the audience exposition maybe for a change

I utterly agree with you on this. I also think she's either the eldest or the sandwhich child which would depend on which year of med school she's in. I think she's probably the eldest of three with the sister being the youngest. Thank God I don't know physics *grin* because then I would have been more annoyed. As it is I took the radioactive shoe as having been tempered - the radiation I mean - by it's trip through the Doctor's body.

Loved the episode.