Slughorn did not consider the "expected" effect. Instead, he worked backward from what had happened, deducing the effect the Potion had actually displayed.
The originally incomplete limb had been repaired into a golden limb.
So what situations in reality happened to people with missing body parts, situations similar enough to correspond to this phenomenon?
Slughorn had a general line of thought. Then, with that idea in mind, he worked backward through the question...
"I think I roughly understand it. But I cannot guarantee that this is definitely the case, since this is an entirely new path you created."
Slughorn did not overstate his conclusion, even though he felt this was the truth.
Just as he had said, this new path, like the previous path that had produced Wolfsbane Potion, had been pioneered by Manus. He had never encountered it before.
As a "Potions Master," the professional help he could provide in this situation was limited. More than anything, he could offer Manus other perspectives from an objective, detached standpoint.
That said, Slughorn still laid out his train of thought clearly:
"I think this problem is essentially the same as the unavoidable tendency toward cosmetic applications that you mentioned with Wound-Healing Potion—have you ever seen dentures?"
"Dentures? Gold teeth?"
Manus had indeed immediately connected this to the source of the problem, but... that did not seem right, did it?
"Do you remember how you said your Wound-Healing Potion had been developed along the lines of Beauty Potions, which was why its healing effect was poor but its scar-removal effect was outstanding? It is the same this time. Wounds naturally heal; Wound-Healing Potion merely makes them heal better. That fits the cosmetic effect."
Slughorn tapped his index finger rhythmically against the rim of his cup.
"But regenerating severed limbs... that kind of