...right. He's being stupid. He reaches forward to grab the inkwell out of the air then brings the stopper to his other hand with the spell.

"Ms. Astrid, what did you just observe?"

"...like... he switched targets?"

"In more detail? What did it look like when he was switching."

"Ah..."

"He started holding the stopper before he'd fully let go of the inkwell," says curious guy.

"Did he? Mr. van Wal, do you concur with Mr. Janus's assessment?"

"...no," says erstwhile-shocked guy. "It was more continuous?"

"Like he was letting go of one and starting to grab the other at the same time, but the total flow of mana was the same throughout," says Astrid, understanding dawning on her.

"Just so! Mr. Vallynn did something that would look very strange, if this were a Skill, but it also looks very strange, knowing that it is not. Why?" This last question is directed at Vallynn himself.

He's being tested again, and he has no idea what the answer is. "Uh..."

"You can figure it out if you think about it," she assures him.

...alright. Challenge accepted, then.

What about what he did was strange if you assumed this is a Skill? The answer is obvious: Skills are discrete, and smoothly transitioning between targets the way he did is roughly impossible to do if you don't know how to do at least most of the work the hard way. Stronger versions of Fire Bolt can fit multiple bolts into a single cast but if all you know is the Skill form of that spell you won't be able to have multiple targets for each individual bolt of a single cast.

And what about what he did was strange if you assumed this isn't a Skill? ...the fact that the total flow of magic was constant in the handoff.

"Please resume floating the inkwell while you think, Mr. Vallynn."

—right yes he does that. With the stopper he feels a lot more confident and less scared he'll dump it all on the floor.

Why was the total flow of magic constant? He doesn't think he was trying to do that... "It just felt natural?"

"What did?"

"The thing where I sort of slid between one target and the other while keeping the amount of magic constant. Like it was a Skill. It just felt natural."

"I'm sure it did. Do you know why?"

"I have guesses."

"Let's hear them."

"Something about how I originally developed the spell with one target in mind and practised with one target in mind so now I kind of subconsciously hold that subjective feeling solid in mind?"

"That seems probable! And there are theories related to the formation of Skills that would imply there are external forces nudging you in the direction of treating spells as discrete units, but if so, these nudges tend to be reasonably easy to ignore or work around. If nothing else, you will almost certainly be able to create less wasteful, more precise versions of this spell if you iterate on it.

"Anything else?"

...is there anything else? He feels inclined to say "no" but he should actually think about it.

"Still guessing, but it's maybe easier to keep a constant flow of magic going than to change it." Which isn't the case for most Skills since they tend to be once and done but then again they basically hijack your body and brain.

"Interesting theory! How would you test that?"

"By trying to change? And seeing if it's harder or not. Except that'd be confounded to hell and back and I'm not sure how to actually isolate it..."