"Trial and error, mostly. I can come up with some low-risk rituals that could work if something's good and fail harmlessly if it isn't, but it'll take me a while to cover all my bases. But I'd probably see if you've got any healing plants first, it is pretty important."
"Hm. I'd probably like to look at those soonish, sir, if they've got baked-in magic. That could be even better than what I've got. But again, I've got a good supply of the vervain and unless someone breaks a leg or something it probably won't go away any time soon." He deems the supply of blood sufficient, plasters his elbow over with a bit of clay he apparently had in one of his pockets, and smooths an airtight layer of stone over the blood in the bowl.
He sets the bowl down. Very slowly, avoiding dizziness, he sketches out a runic circle around himself, throws a pinch of powdered root into the air, then intones a few minutes of vague Germanic chant about the wholeness of the body and the blessed restoration of vitality and so on. A faint red glow branches out from his chest along his body, and by the end he looks a bit less ashen. He strips the clay off his (no longer bleeding) elbow and melds it back into the supply in his pocket.
In that case, Ari can return to his work on the ritual and his valiant attempt to explain his work to the fairy. It's actually kind of a good thing, he explains, that there are no animals, because using his own blood means more power will go into the circle. Which makes things a bit easier.
"Ooh." Ari wasn't going to mention it, because it seemed a bit of a faux pas to suggest bleeding one's master, but he's glad it's an option on the table. "I could test it with... hm. If you don't mind possibly being flashed with a very bright light if it turns out your blood is more potent, there's a simple pyrotechnic illusion I could incorporate it into. How does that sound? It'd only take a small cup's worth, I can heal you up the same way I did for me."
"Best test that, I think," Ari says cheerfully. "I can prick you with a pin or something and we'll test it that way?"
...Ah. Inconvenient. For a few reasons, not all of which Ari is going to mention. "You could prick yourself then?"
There are people who don't get along with him, but they generally eat babies. Or they don't like his habit of saying spectacularly insensitive things, one or the other.
"Yes, sir."
He closes his eyes and forces himself to breathe the way Belinda taught him when he was this angry back home. Her smooth voice fills his head, repeating the mantra she taught him.
Ice and fire, ice and snow. Hate, but never let it show. Ice and fire, ice and snow. Hate, but never let it show.
Slow, careful words. Even, careful tone. Ari's face arranges itself into absolute neutrality. "I was afraid, and my magic reacted. It does not happen often. I can calm myself with a few moments to breathe."
He erases the crushed rune with an incantation in a whispered monotone. He draws it properly, line by line. He considers the next, sketches it in the same way. As he continues down the row, he regains his easy speed. He breathes naturally. After two more rows, he begins to explain what he's doing again.
"Could I please have some food, sir?"