I enjoy sketching people when they're talking and moving around. This is Harmon Simmons (1931-2013), a tour guide at the Vanderbilt Mansion in New York, back in 2001.
He described himself this way: "I'm Irish, Dutch, English, and Indian—Duke's mix. Open the can and I come out."
Doing a sketch of a highly animated person means choosing a characteristic expression and locking that expression in the short term memory as the person moves around.
Harmon Simmons obituary