What do you think of one species of animal nursing the young of another species?

The wording of the question is strange, but I didn’t know how to phrase it. If you look anywhere on the internet, there are stories of animals nursing the orphaned young of other species of animals:dogs nursing cats, cats nursing rabbits, rabbits nursing skunks, etc.

I think animals are more sentient and intelligent than us humans believe. Is this just some sort of instinct, do the animals know the difference, is it a result of domestication—the instinct to hunt and kill being suppressed due to the availability of food and protection, or what? What do ya’ll think. I’d really be interested in some feed back from the science people in the collective.