A good listener maintains eye contact and leans slightly toward the speaker. Their facial expression shows interest and indicates they understand what is being said. They smile, nod appropriately and use other positive gestures. They ask questions to clarify points, but do not interrupt. And they paraphrases or restates important points to insure that they understands.
Most people dislike to be interrupted.
While that mannerism may be acceptable in some homes, it is never acceptable in a business situation. A major reason why people interrupt is that their minds are racing faster than the speaker's words. A person thinks about 600 words per minute while even a fast speaker talks between 100 and 140 words per minute. It may be tempting, but one shouldn't mentally argue points or rehearse answers while the other person is speaking. They may miss something very important.