"For that matter, if you want to make a serious study of local magic, the person who can come up with a functional permanent sunlight ward in two hours is probably a better teacher than an unattended library if they are capable of teaching at all."
"Anyway. I am thirsty and would like to spend the first part of our two-hour wait stealing blood from a butcher's shop."
"Should I supervise you so the Slayer doesn't hold me responsible if you have a sudden lapse of judgment?"
"Well, I don't have anything else to do anyway." She flutters into the air to follow him.
He locates the back entrance of a butcher's shop, picks the lock, enters, and raids their supply of animal blood.
What's that over there?
It appears to be a couple of mortals making out in an alley!
"I think I've seen that fellow around before. Mind if I stop for a chat?"
He approaches the pair, casually sipping from a large plastic container full of pig's blood.
They're pretty well occupied, but during a break in the proceedings one of them turns around to call out at him, "Hey! Find your own alley, we're busy here!"
"...What is that?" wonders the other alley-goer.
"Pig's blood," Tea says cheerfully.
"Ew! Gross!"
"I don't think I know you," the blond one says dubiously. "And hey, rude. We were having fun here."
"Okay, I'm done here," says the brunette. "You have weird friends." She turns to leave.
"I've got extra," he says helpfully, hefting the paper bag containing two more containers of blood.
"I suppose I could also compensate you for other losses, if you insist."
"I think you're right, we haven't met before. I'm Sherlock," he offers.