Having had magizoology rather on the brain of late, I have just bought, and read for the first time, "Fantastic Beasts and Where to Find Them". One such creature struck an unexpected chord with me -- the Nundu: "This east African beast is arguably the most dangerous in the world. A gigantic leopard that moves silently despite its size and whose breath causes disease virulent enough to eliminate entire villages, it has never yet been subdued by fewer than a hundred skilled wizards working together."
A book I read long ago, was "On the Track of Unknown Animals" by Bernard Heuvelmans. It dealt at varying lengths, with an assortment – from most of the world's continents – of creatures reported in varied ways, but as yet unknown to science (including a very long chapter on the Abominable Snowman). This book's coverage of Africa included a briefish section on a crypto-beast known as the "Nunda" or "Mngwa", whose supposed characteristics closely match JKR / Newt Scamander's description (less the part about the appallingly lethal breath). An unclassified big cat (black, IIRC) said to live in the forests of East Africa – highly aggressive, with man-eating not an aberration, but standard behaviour for the species – inspiring great terror of the creature, in the locals. An indication seen, that JKR has likely read Heuvelmans's book!
Would stress that I am in no way complaining about JKR's having possibly got the inspiration for this item in the bestiary, from the source suggested, rather than 100% from her own imagination – any more than I would belittle Lewis Carroll for the fact that March hares and supposedly-mad hatters existed in adages; and Humpty Dumpty in a nursery rhyme; before he put them into his works. I was just delighted by the indication that our author may well be familiar with a book which, in my early teens, at once fascinated me and gave me the creeps.
