Romana sniffed experimentally at the mysterious jug in their fridge, wondering why the Doctor had decided to bring it home and whether it was really something to drink. Gallifreyan food was much more sensible; it was always clearly labelled and it never did anything as silly as going off if you left it out. You opened it and you ate it. Admittedly, it never tasted quite as nice as Earth food could. Although Earth food didn't always taste very nice either when it was her and the Doctor cooking it. She hoped perhaps they would learn to cook in the time they were here. Fortunately for the meantime, Glenda in the flat next door had brought them a casserole. (Out of pity, no doubt, after she'd caught Romana trying to open tinned soup with a knife. Well, the Doctor had said he didn't think the tin opener had been invented until 2034—how was she to know she could've used one?)
The jug in the fridge was labelled "MILK 1%." Milk she knew—it was something you put in tea. But she rarely made her own cups of tea—the Doctor prided himself on both his ability to make a good cup of tea and his ability to get people to offer them one—and so she wasn't very familiar with milk. It came in lumps, didn't it, or was that sugar? And anyway, it said it was one percent milk. What was the other ninety-nine percent?
She took an experimental sip of the smooth white stuff and wasn't sure what she thought. It didn't seem very nice at first—it tasted like it came from some kind of animal—but it was creamy and a bit sweet. Hopefully it was actually milk as in tea and not something completely different which went by the same name. She put the cap back on the jug and put it back in the fridge.
When the Doctor got home a bit later, she laid aside the field journal she'd been working on and made a point of asking him about the MILK 1% jug first thing.
"Oh, it's milk all right," he said, somewhat amused. Well, it was a perfectly valid question, thought Romana indignantly. He explained to her the meaning of 1% butterfat, and also the connection of milk and butter, and then the origins of milk in the cow.
"How primitive," she said, wrinkling her nose. "And all mammals do this? Thank Rassilon we belong to a civilized species."
"Don't give Rassilon all the credit," said the Doctor drily. "Fortunately it's only cow's milk you and I have to worry about."
"I'm not sure how I feel about that," she said.
"Oh, never mind," he said. "It gives us cornflakes and cocoa and lovely cream teas. And milk mustaches."
"Milk mustaches?" she asked, intrigued by what she supposed to be another human food.
He grinned and whispered, "Look in the mirror."
She did. And turned back to him saying, "You might have told me!"
"But you look so lovely with it on," he said coaxingly.
She laughed and forgave him.