Lilu was tempted to cast a wandless hex that would cause Sirius' nose to itch uncontrollably. Relatively harmless, but amusing, and would serve him right for looking down at her that way. He wasn't that much taller than her, sneering down like that should have been impossible. She hated that he made it work. Bloody overgrown bat.
"Weeeeelll," she dragged out the word as long as she could, being deliberately annoying mostly because it was fun. Well, fun for her. Hopefully not fun for Sirius. "Theo and I are in need of ingredients. Wand wood, cores, you know. All the necessities for making wands." She grinned, pausing for a few moments. Again, just to be as annoying as possible. She wouldn't want to make this easy on him. Though, in a way she was only hurting herself because the longer this took, the more time she had to look at the greasy git. "As it turns out, unicorn hairs are proving to be difficult to collect without a virgin along. So we thought we might take a survey, see if anyone would be able to help us with this particular ingredient."
She grinned, meanly even though she knew Severus would sigh at her when she told him. He wanted to play nicely with Sirius for some Merlin-forsaken reason. "Naturally, I thought of you."