Telling a story. Now this was something that Martha was good at. She prefaced what she was about to say with a standard qualifier. "I know it sounds completely mental" because it did, "but the TARDIS is this ship thing that I traveled on for a while."

Martha paused as he gestured towards the table, and she moved over to sit on it. Doctors were generally the worst patients that there were, so she had actually spent very little sitting upon an exam table.

"Because it travels through the time vortex, it means that there's all this background radiation that seeps into your cells when you do it. It means that I'm not allergic to anything, and I can't catch plagues or what not. It also means that any germs I'm carrying aren't going to be harmful to the times or people whom I've visited."