Yes, eventually they're bound to become immune to each other, or something. Right?

She arches an eyebrow at him and nods slightly. Guess who won't be taking aspirin. She'd rather put up with a bit of a headache then not be around them. She relaxes a little bit when he does go ahead and hold the ice against her cheekbone. "Time Lord thing? Or you thing?"

Because not all humans are allergic to strawberries, for example, just a large number of them. Also, she realises that he's probably lying about the ice pack but it's also not going to kill him and she understands he's punishing himself a bit by not using the ice pack. She'll let it slide. This time.