"Don't be silly, Doctor," said Vicki. "The sniper won't be looking in my room, will they? And if they shoot me, in yours, with the weapon tuned to your personal bioprint, it won't do me any more harm than ordinary infrared waves, you said before. So we should swap."
"It makes sense," the Doctor admitted reluctantly. "But what if the assassins attack at closer range? Even if they see you're not me, they might break in and attack."
"Oh, don't worry," she said cheerily. "The Doctor—I mean the other Doctor, the old gentleman—he's been teaching me to box!"