At the positive reaction, her scratching became surer. Really, Renne was reminding her of a big blue alien cat.

Ah. That explained it, though she still wasn’t clear on how biting something would help identify it. Perhaps it was a non-human thing, like the Doctor’s licking of things (though she half-suspected he did it to embarrass her/weird her out, depending on what he was licking and if they had company).

“Don’t get blue boxes around there often?” Assuming this alternate TARDIS was stuck as a police box. “Or blue leather?”