This is Rose. She is a human, at least so far. She is traveling in close quarters with the Doctor, who is not a human. The Doctor brushes past her, his wiry arm reaching over her shoulder carelessly to turn a small shiny crank. As he futzes intently with the control, he leans in further.
Rose is watching him tinker, and woefully wondering if this Tardis thing will ever correspond to any pattern of sense or logic. She knows the Doctor turns the big crank and it makes a great big grinding noise when it goes somewhere, and that is the extent to which cause and effect seem to have to do with it. The hand that's not reaching over her gives a pat to her bum — absentmindedly, no less — and she startles.
"What! Doctor, you don't fancy me, do you?" She says it as a joke, so he can leave it at one if he wants to.
"No!" he shouts. "How could I possibly fancy you? That's ridiculous!"
Rose is furious, but catches herself. She really doesn't think, after all, that he means the same thing a human her own age would mean by that vehement response. "Well," she stammers, "Uh… Mickey always told me I had nice tits."
"Tits? Well I suppose they can be nice, but I was never much for that ornithology stuff." He pays attention to a readout, whacks it backhanded, turns back to her for her response.
"No!" She bites her lip, suddenly self-conscious. "Tits like - breasts. You know."
"Really?" All of a sudden the Doctor is wide-eyed interested, advancing slowly towards her. "I know the females of some species have those, but I didn't know that humans did. I mean, most people just have a faux frontispiece. They can get very elaborate."
"No, female humans definitely have breasts," Rose informs him.
He frowns. "I'm not sure I believe you. It's very popular to claim that sort of thing. You just don't see real ones very much."
"Go to a table-dancing bar in London," Rose says.
The Doctor says, "Okay!", strolls over to the big crank, and starts firing up the Tardis.
"No," says Rose, "no, don't, you don't have to bother." She's still looking forward to seeing the fifteenth century, and really, upon thought, does not actually want the Doctor to go to a table-dancing bar in London.
Rose lifts up her blouse, pulls the bra cups up. "Here. See? Human females have breasts." She jiggles them at him demonstratively, then puts the whole thing back on. Only, when she looks up, he's doubled over with laughter.
"What?" she says, suddenly uncertain. "What?"
"I got you to show me your tits!" he crows.
Rose looks at him with a dry expression. "Then they're really quite common, I take it."
"Absolutely mundane. I got you to show me your tits!" The Doctor collapses with laughter again. The whole Tardis seems to shake with it.
Rose feels like thwacking the dirty old madman upside the head, and then she comes to a realization. She grins. It's a very smug grin.
Now is the Doctor's turn: he was clearly expecting her to be badly put out. He looks awfully nonplussed. "What?" he says. "What?"
"You do TOO fancy me," Rose says.