I once got two kittens from a kill-shelter. They were tiny, runted 3-4 weeks old, could fit in the palm of my hand with room to spare! They were in the "kill cage" and slated to be put down very soon because of their coloring and sickliness. I took them home with me and was it ever a chore! They knew nothing about using a litterbox, dry catfood, playing with toys, climbing. I had to feed them formula and wetfood and build up to dry food (eventually they turned into little piggies!), I had to put their paws on objects and move their bodies to teach them to climb, bat at toys, etc. They were thin as rails, stuffed to the gills every form of worm imaginable, one kitten had it's whiskers shaved off, and the other had an abscess in it's leg, plus a world record amount of earmites. They eventually survived but were never "normal". The boy cat hated the house and when given the opportunity, merrilly adopted the barn as his haunt and has a grand time tearing up the outdoors. He tolerates people but prefers to be a loner. The other cat became desperately attached to a little boy that visited and refused to leave his sight. I ended up giving her to him to prevent an feline breakdown when he left. She is now living it up in Florida, absolutely worshiped and adored by her new family. Which is a good thing, because I could not litter train her to save my life and the new family ended up putting chicken wire around their beds to keep her from using them a dumping ground. Then and only then did she use a litterbox, and then as a last resort.