from "tadpole," the immature form of a frog + "foal," the young form of a horse
The Muggle name for the sleepless three-headed dog who according to mythology guards the gates of Hades is "hellhound." The three-headed dog's name was Cerberus, and the only time when he was ever overcome save by brute force was when the great musician Orpheus sang him to sleep.
Toads are allowed as pets for students at Hogwarts, but they're out of fashion, so if you have one, you're likely to be laughed at for it. Nevertheless, Neville has a toad named Trevor, a gift from an older family member (PS6, Pm), and there are enormous purple toads in the Magical Menagerie (PA4). Furthermore, judging from Mundungus' story on Harry's first night in Grimmauld Place, toads (at least in bulk) are valuable enough to go to quite a bit of trouble to steal (OP5).
- Ron has a frog in a tank in his room (GF5), and the pond in the garden of the Burrow is full of frogs (CS3).
- Petunia accused Lily of coming home from Hogwarts with pockets full of frog spawn (PS4)
- c.f. horned toad
Dudley once threw his tortoise
through the greenhouse roof
The gigantic tortoise with jewel-encrusted shell that Harry, Ron, and Hermione saw in the Magical Menagerie was probably a Fire Crab (PA4).
There are three types of trolls: mountain, forest, and river
Troll language supposedly consists
of grunting and pointing
(GF7), but that description is
courtesy of the Weasley twins, who were
attempting to wind up Percy on the
subject of his boss' linguistic ability at the time.
The mountain troll is very stupid. It stands twelve feet tall, with grey skin, a lumpy body, and flat horny feet. It exudes a powerfully awful smell, "a mixture of old socks and the kind of public toilet no one seems to clean." Its nose is full of what looks like lumpy, gray glue: troll boogers (PS10).
Quirrell, to create a diversion so he could go after the Philosopher's Stone, let a mountain troll into the castle on Hallowe'en, 1991. It wandered around the corridors until Harry and Ron locked it in a girls' bathroom. Right after they did that, they realized that Hermione Granger was in that particular bathroom, and they had no choice but to charge in after it. With a lucky combination of derring-do, desperate magic, and sheer dumb luck, they managed to knock it out and save Hermione (PS10).
Quirrell, it turns out, has something of a knack for handling trolls. He placed one in the chambers guarding the Stone, knowing he'd be able to knock it out quite easily when the time came. By the time Harry, Ron, and Hermione arrived in that chamber, the troll was out cold (PS16).
Tom Riddle alleged that Hagrid, as a boy, would go into the Forbidden Forest to wrestle trolls (CS17).
Trolls participate in wizarding society to some extent; some witches and wizards make a career out of training security trolls (OP29). Dumbledore hired security trolls to guard the Fat Lady after Sirius Black attacked her. These were evidently a different type of troll than the mountain variety, since they seemed considerably more intelligent and less smelly. They spent all their time pacing the corridor in front of the Fat Lady's portrait, giving dirty looks to everyone who happened by and comparing the sizes of their clubs (PA14). Umbridge apparently also hired security trolls to guard the Firebolt she had confiscated from Harry (OP30).
Trolls are not recognized as magical beings (FB). Pierre Bonaccord, the first Supreme Mugwump of the International Confederation of Wizards, wanted to stop troll-hunting and give them rights, but his appointment to that office was contested by Liechtenstein, since they were having problems with a tribe of very dangerous mountain trolls at the time (OP31). The Black family kept an umbrella stand made out of a troll's leg in their front hall (OP4). A large stuffed troll can be found in the Room of Requirement when it is in "lost objects" mode (HBP24).
Hagrid and Madame Maxime ran into a couple of mad trolls on the Polish border while on their journey to visit the giants (OP20).
Note that OP31 does not capitalize "mountain troll" in the U.K. edition, so the term should not be capitalized.