Many body parts are involved:
One reason why human speech communication is so powerful, complex, and efficient is that the human body is anatomically designed for optimal speech communication. The human lungs, larynx, pharynx, vocal cords, mouth, and lips are optimized for uttering a wide range of distinct sounds at a rapid pace. The human brain is designed for complex language capability and for multilingual capability. Human legs and feet are designed to set the arms and hands free from locomotion. Human arms and hands are capable of amazing dexterity and eye-hand coordination and rapid, repetitive movements. The eyes of humans with irises and pupils set against large white spheres (a feature not shared with nonhuman primates) permit signaling between humans over distances of many meters. The human face is capable of a wide range of expressions.
The human body is optimally designed for speech communication involving just a few people in a quiet setting. It also is optimally designed for what researchers call “cocktail party listening.” Cocktail party listening refers to humans gathered in a crowded situation where many people are talking simultaneously in an environment where music and other background sounds interfere with speech recognition. Researchers have noted how well-designed human brains and human bodies are for selective listening.
Hugh Ross, “Does Complex Speech Expression Demonstrate Human Exceptionalism?” at Reasons to Believe (April 5, 2021)
We didn’t realize that anyone listened at cocktail parties. But come to think of it, if you were one of the few people who did listen instead of just talking…
See also: The real reason why only human beings speak. Language is a tool for abstract thinking—a necessary tool for abstraction—and humans are the only animals who think abstractly.