|Muggles' Guide to Harry Potter - Magic|
|Features||Looks like a hedgehog|
|First Appearance||Harry Potter and the Order of the Phoenix|
The Knarl is largely indistinguishable from a hedgehog.
The Knarl is mentioned three times in the series. The first time, in Harry Potter and the Order of the Phoenix, is when Professor Grubbly-Plank is being inspected by Professor Umbridge. Responding to a query about her course plans, Professor Grubbly-Plank says that she still has to teach the class how to detect Crups and Knarls.
Later that same year, Hagrid, then teacher of Care of Magical Creatures, expresses his dissatisfaction with the Ministry-approved curriculum by saying he can't understand why anyone would prefer learning about Knarls instead of Chimaeras.
The final instance, in the same book, is when Harry, in his Care of Magical Creatures OWL, must distinguish Knarls from Hedgehogs; we are told that he did this by offering them milk.
In Fantastic Beasts and Where to Find Them, "Newt Scamander" tells us that the only difference between Knarls and Hedgehogs is that, offered food, a Knarl will believe that it is a trap and will react angrily.