What is the essential difference between human and animal intelligence? I don't actually think it's just a matter of degree. To put it simply, most brains are once-through machines. They take input from the senses, process it in conjunction with memories, and turn that into actions, and perhaps new memories. Their brains have lots of special-purpose optimizations for many things, and a surprising amount can be achieved like this. The brains are once-through largely because that's the fastest approach, and speed is important for many things. Human brains are still mostly once-through.

But we humans have one extra trick, which is to do with self-awareness. We can to an extent sense the output of our brains, and that output then becomes new input. This in turn leads to new output which can become input again. This apparently simple capability - forming a loop - is all that's needed to form a Turing-complete machine out of the specialized animal brain.

Without such a loop, an animal may know many things, but it will not know that it knows them. Because it isn't able to sense explicitly about it was just thinking about, it can't then start off a new thought based on the contents of the previous one.

The divide isn't absolute, I'm sure - I believe essentially all mammals have quite a bit of self-awareness, but only in humans does that facility seem to be good enough to allow the development of a chain of thought. And that small difference makes all the difference in the world.