It took the Doctor a minute to realise that Martha wasn't watching him, or watching the time rotor, or any of the things she usually did when the TARDIS was in flight. Instead, she was... staring intently at the console itself. The Doctor stopped, and frowned at her. "What... what're you doing?"
"Is... is that a heart probe?"
"What?"
"Right there," she said, pointing. "That's a heart probe, isn't it?"
The Doctor moved around the console to see what she was pointing at. "That's a switch," he said, doing everything he could to imply she was just being silly. "'s why it's on the console."
"Yes, and you've also got a bicycle pump. What was it before it was a switch?"
The TARDIS rocked, and the Doctor bounded around to the opposite side of the console to steady it. "It was... a heart probe."
"So what, do you just walk into hospitals and take random things when you need to repair your spaceship? You can't do tha-"
"Oh, I didn't take it! I just sort of... pulled it out of me. Out of my heart."
Martha's eyes widened as she leaned around the console to stare at him. "And you just kept it?"
"Well, I did try to give it back. The doctor who put it in me wouldn't take it. Since you're standing there, would you mind flipping that switch just about... now?"
She looked down at it mistrustfully, like she thought it might bite her. "Do I actually have to, or do you just want to make me touch it?"
"Well, unless you want to crash into the 1980's..." He broke off as the TARDIS shuddered, grabbing onto the console to keep from toppling over and waiting a moment for the TARDIS to steady before he spoke again. "Too late."