As a biologist, one of the things you get to learn and practice a lot is looking really closely at things in nature, describing them and comparing them to each other. Where once you saw "some grass" by the side of the road you now see 11 distinct species, you can name each part of the plant and you know exactly where and what to look at in order to find out if it's a meadow fescue (F. pratensis) or sheep fescue (F. ovina). Suddenly you are much more aware of all the many subtle differences in previously mundane things that you have been around all your life, and you even have distinct names for them now. The striking effect this has is how much more you notice.  


If you have ever lived or worked with two parrots of the same species, you'll recognize this phenomenon. 
As an example, meet Rio:


Rio was one of 12 rainbow lorikeets in a walk-in aviary that I used to work with as a zookeeper.

One of the most common questions I would get was how on earth I could tell them apart? They looked identical to most people, but since I worked with them so often I could easily tell who was who based on subtle differences in their color patterns, facial features, beak sizes and their behavior.  

To most people who visit the zoo however, Rio is "a bird." To some that might recognize the curved beak and lively colors, he is "a parrot" which is a kind of bird. If a parrot enthusiast is visiting he might be a "lorikeet" or even a "rainbow lorikeet" which is even more precise.
Someone else might have experience with their friend's blue and gold macaw, and ask if Rio is a macaw. This might seem like a very silly question to someone that is used to parrots, but it actually makes a lot of sense based on that oerson's past experience. They have learned that a bird that also has a curved beak and a lot of pretty colours is a macaw. They don't have experiences with birds sharing those same features being called anything else but a macaw. Why wouldn't this bird also be a macaw?


Being able to differentiate - noticing if and how something is different from something else is a matter of having the right concepts for something, and of learning what to look at to differentiate it from something else. I can easily tell you if a Buttercup is an R. repens or R. acris and describe what the observable difference is (it's the length of the odd-pinnate rachis!) but if you asked me to tell a Hyundai from a Toyota I would have absolutely no idea how to do that or what to look at.

Body language is full of nuances that we need to learn to differentiate between. We can say that body language has a lot of granularity. Sometimes a small detail can make a huge difference in how we should interpret or respond to behavior. The more we practice watching parrots, the higher our observational "resolution" will become - in other words we learn to more easily and accurately spot when relevant details are or are not there. 

You might recall this picture from section one: 


A very "coarse" description of what we see here might be "an open beak." 
This is absolutely correct, and sometimes that's all we need. Other times, we need more fine-grained information. "The beak is open wide and the tongue is tucked in the back of the mouth."
We see open beaks in a lot of different contexts, such as when parrots are eating, chewing toys, investigating and even preening. With just that tiny bit of extra information - that the beak is open wide and the tongue is tucked - we can narrow our scope and cancel out a lot of "noise" about what is going on. Wide open beaks occurr in much fewer situations, and the combination of a wide open beak and tongue tucked back, in even fewer still. There's no point in being more fine-grained in your descriptions than you need to be at any given point. However, there is definitely value in being able to describe behavior with varying levels of detail. Sometimes a course description is all we need, and sometimes we really need to look at the fine-grained details in order to tease out what is what.