Pika. Pika, Pika. While Pikachu's vocabulary might seem limited, its impersonations aren't.
Japanese Twitter user Puijiro uploaded this "Collection of Pikachu's Facial Impressions", using Pokémon anime images from over the years. So far, it's been retweeted over 38,000 times.
Have a look:
Now this is a true Pokémon Master.