Well, to be clear there ARE many things that make us unique, but they work as a combination. For example, a rat isn't unique for having fur, but thousands of other animals lumped together into a group are. But then you might find an exception, a reptile with fur or something - but its different on so many other levels that it doesn't fit into the group.

What makes us a species is usually a collection of features, and that's why it becomes so hard to classify

Thanks for being part of this long journey!