Parrots are able to mimic human speech and sounds due to their unique vocal anatomy. They have a specialized vocal organ called the syrinx, which allows them to control the muscles in their throat and produce a wide range of sounds. Parrots are also highly intelligent and social birds, which enables them to learn and mimic sounds they hear in their environment, including human speech. Additionally, parrots have a keen sense of hearing and are able to accurately reproduce sounds by listening carefully and practicing them over time.