This is a heartwarming animal video about a mother cat who has adopted a baby squirrel, and nurses it with her own kittens. Apparently the squirrel now makes purring noises and behaves quite differently from ordinary wild squirrels.
As pet owners know, there's a huge amount of variety in the way animals even within one species behave, based on their upbringing and the situations in which they've developed. I'm not so much thinking about the purring here, but the general indoor behavior of the squirrel. (On that note, there's an interesting story about social norms in savanna baboons that I wanted to link but it's behind a paywall so see the short version here.) It's the most extreme in humans, the champion learners of the animal kingdom, but it's true all over. It adds to my skepticism about claims that humans are hard-wired to perform that many highly complex social phenomena.