One of the most successful animal species to colonise the Discworld. Felis Domesticus, by devious routes all of its own, has managed a symbiotic relationship with Homo Sapiens in every part of the galaxy that Man has made his own.
The contract between Cat and Man is clear. The human signatory is expected to provide, on demand, ample qualities of:
iii) Dry comfortable sleeping places;
iv) toilet facilities of the feline party's choosing;
vi) maternity facilities for occasional kittens.
In return for this, the feline party consents to occasionally turning up (as and when it feels like it), and kindly condescends to make a show of what the human party misinterprets as affection every so often. The feline party will also undertake to excrete or spray in inappropriate or inaccessible places and at inappropriate times, and to deliver gifts of fresh - well, fairly fresh - entrails as and when appropriate. The human party is not to complain about this as, well, you hang game for a few weeks because it tastes better, don't you?
On the Discworld, other humanoid species are baffled and bemused by the human susceptibility to cats. Trolls have learnt by now to stop trying to eat cats - even though they cannot be actually harmed by a bundle of spitting fury en route to those diamond teeth, it is still a disconcerting experience to find the nice handy meaty snack you have just picked up is screaming blue murder at you, wriggling and squirming to free itself and simultaneously making every attempt to put a permanent scratch across the thick silicon quartz lenses of your eyes. It just ain't worth it, even for those health-giving trace minerals, so cats are now avoided. This leads to amusing encounters such as that in Maskerade between Detritus and Greebo in his were-human form, where in the shape of a cat he still retains enough human sentience to rasp "Get lost, copper!" at the troll, which causes a certain existential confusion in Detritus' slow-moving troll brain.
If such creatures as troll cats exist in the fastness of the mountains, one almost certain prediction that can be made about their behaviour is that they will, out of love and respect, leave mouth-watering fragments of troll ducks and other silicon-based prey in the sleeping areas of favoured trolls. However, references in the chronicles of Discworld suggest that there may be no such life form, which would be a shame.
Feline domination apparently has not only touched humans, but seems to have affected the more supernatural beings. Death himself is known for being overly fond of kittens, though this habit seems more transitory than most human cases.