Here are three interesting references by Hogwarts' Potions master in HBP that give us new canon information, a hint about the nature of a particular medical potion, and an in-joke:
"I was just telling young Marcus here that I had the pleasure of teaching his Uncle Damocles," Slughorn told Harry and Neville, now passing around a basket of rolls. "Outstanding wizard, outstanding, and his Order of Merlin most well-deserved. Do you see much of your uncle, Marcus?"
:::
"Not. . . not much of him, no," gasped Belby, his eyes streaming.
"Well, of course, I daresay he's busy," said Slughorn, looking questioningly at Belby. "I doubt he invented the Wolfsbane Potion without considerable hard work!"
It's always been theorised by the fandom that Snape invented Wolfsbane Potion. Now we know that he did not: Damocles Belby did.
Damocles is listed in the World Book Online. Here's the article:
Damocles was a member of the court of Dionysius II, who ruled Syracuse, Sicily, from 367 to 344 B.C. Damocles was an excessive flatterer. The Roman orator Cicero said that Damocles once talked too much about the happiness and good fortune of Dionysius. To teach Damocles a lesson, Dionysius invited him to a big feast. When he was seated, Damocles found a sword, suspended by a single hair, dangling over his head. This sword represented the constant danger that went with the wealth and material happiness of Dionysius. The sword of Damocles has become a byword for the threat of danger.
The Wolfsbane Potion might well be designated as the sword of Damocles in the series, for wolfsbane, or aconite, is, in real life, deadly poison. Yet it's this poison that gives some measure of comfort to werewolves by allowing them to retain their own minds. The potion is both problem and solution.
But wait! The sword of Damocles, in legend, threatened Damocles himself. Is it possible that the Potterverse version of the sword of Damocles--Wolfsbane Potion--was invented by Damocles Belby because he's a werewolf? If so, the potion would present the same razor-edge danger and treatment as the legendary sword did.
And one more thing...we learn about Damocles Belby because of his nephew, Marcus.
Marcus Belby.
Am I the only one old enough to remember
Marcus Welby, M.D.--a TV show about a kindly old general practictioner who was dedicated through and through to the welfare of his patients?
(And ironically, young Marcus knows almost nothing about his uncle, who is truly the dedicated and thorough one in the Belby family, simply because Marcus's father and uncle don't get along.)
I don't think that all this was done accidentally.