"The details of his methods are often pure fiction, but the basic principles are sound."
Pause.
"What'd you get me for my birthday?"
"Is it too late and/or too soon to offer you Arthur Mallory's head on a plate?"
"Didja get me anything? Is there a box hiding in this house somewhere that you were going to give me except that our evening got derailed?"
Is "expectant snuggling" a thing? Because she does that.
...
"Unless you'd rather get up. Because you can if you want."
Judging by size, shape, and weight, he got her a bowling ball.
Bella smiles at him, sets the present on her lap, and tears into the wrapping paper.
"You did mention magical artifacts," says Sherlock.
"It's beautiful - what does it do?" asks Bella, reaching out towards it but not quite touching it lest she leave fingerprints.
"If you hold it in both hands and look into it, it will show you something that you will find useful to whatever degree you understand it. No guarantees about the understanding it part, which is why I was able to get it on eBay for a pittance."
"eBay?" giggles Bella. "There are working crystal balls on eBay? That's hilarious, how did you know it wasn't a fake? And the something - is it supposed to be past things, possible futures, present things, metaphors, some mix?"
"Any or all of the above. I traced its history, of course. And when it arrived it very helpfully showed me all the parts I couldn't verify for myself."
"Oh, that's nice of it. Hello, friendly crystal ball," she says, cupping it in her hands.
"I think this is happening now," she murmurs. "I think they're freaking out because Arthur hasn't called and they don't know if I'm dead - that one thinks I must be alive because they still, heh, can't find the Slayer, and it would just be impossible for two in a row to have my, heh, little problem..."
She giggles and sets the crystal ball down. "That's really neat. And it's not even redundant with mint powers; they're not so good at information. Thank you."