What does "do this" refer to?

[yamyam]

Hello, teachers.

Would you read the following?

"Body language" is unconscious and is used to communicate not ideas, but our inner mental and emotional state. Our faces, body movements and use of space all reflect how we feel. Many people can easily tell if a friend is not feeling happy simply by looking at him or her. When people do this, they are reading the other person and the environment, but usually without knowing exactly what gives them the impression that the friend is not happy. It could be a subtle facial expression, body posture, being somewhere unusual for that person (sitting alone on the ground, for example), or the lack of normal behavior. All of these things are felt emotionally, and they don't depend on language.

Here are my questions:

1. What does "do this" refer to?
Does it mean "tell if a friend .... him or her"?
Or, does it mean just "looking at him or her"?

2. What is left out in the phrase "usually without knowing"?
Is "people tell if a friend ... him or her" left out?

3. What does "It" refer to?
Does it refer to "what gives them the impression that a friend is not happy"?

I'm rather confused about the context of this passage.

I'd really appreciate it if you'd help me with these.

Thank you very much in advance for your help.

yam.

[Bennevis]

"Body language" is unconscious and is used to communicate not ideas, but our inner mental and emotional state. Our faces, body movements and use of space all reflect how we feel. Many people can easily tell if a friend is not feeling happy simply by looking at him or her. When people do this, they are reading the other person and the environment, but usually without knowing exactly what gives them the impression that the friend is not happy. It could be a subtle facial expression, body posture, being somewhere unusual for that person (sitting alone on the ground, for example), or the lack of normal behavior. All of these things are felt emotionally, and they don't depend on language.

1. What does "When people do this" refer to?
When people look at him or her...

2. What is left out in the phrase "usually without knowing"?
But they usually don't know what gives them the impression that the friend is not happy.

3. What does "It" refer to?
Does it refer to "what gives them the impression that a friend is not happy"?
Yes.

There you go.

[yamyam]

Thank you very much for your quick reply, Bennevis.
It helps me a lot.
Thanks again,

yam.

[Raymott]

My responses in blue.
Hello, teachers.

Would you read the following?

"Body language" is unconscious and is used to communicate not ideas, but our inner mental and emotional state. Our faces, body movements and use of space all reflect how we feel. Many people can easily tell if a friend is not feeling happy simply by looking at him or her. When people do this, they are reading the other person and the environment, but usually without knowing exactly what gives them the impression that the friend is not happy. It could be a subtle facial expression, body posture, being somewhere unusual for that person (sitting alone on the ground, for example), or the lack of normal behavior. All of these things are felt emotionally, and they don't depend on language.

Here are my questions:

1. What does "do this" refer to?
Does it mean "tell if a friend .... him or her"? Actually it means this.
When people "tell if a friend is not feeling happy simply by looking at him or her" "they are reading the other person and the environment".
If it meant simply looking at someone, it would not have the connotation of "reading".

Or, does it mean just "looking at him or her"? No.


yam.

R.

[yamyam]

Thank you very much for the additional instruction, Raymott.
Uh, I didn't notice what you pointed out.
Your explanation is quite helpful for me to understand the part.

Thanks again,

yam.