If you want to read a person's mind to find out if he is interested in your words or not, then do these things
In the middle of your conversation, if the person imitates your movements and folds his arms like you, then yes he is interested.
If the person's feet point towards you, they are interested, and if not, they are not.
If the person is looking at things around him instead of you, they may not be listing you properly.
If the person yawns in the middle of a conversation, he's definitely not interested
If a person puts his hand on his neck, it means that he is feeling uncomfortable and does not want to go further.
If they put their hand on their chest, it means that they are honest with you and are talking to you with all their heart.
If the person puts his hand on his head, it means that he is having difficulty understanding you.