A fantastic little deleted scene that I personally feel is required viewing between The Parting of the Ways and The Christmas Invasion. It makes Rose's actions and reactions in the Christmas special more understandable and sets a good basis for the new Doctor. Tennant is still coming into his own, but the base of what the Tenth Doctor will become is all there. A two-line exchange also lets us know that Rose didn't immediately forget about Jack, and it was the Doctor who chose to leave him behind.