Perhaps the most underappreciated of the comedic arts, improv can also be the most difficult — and rewarding. Hot on the heels of the Vermont Comedy Club’s summer sketch comedy revue, the Big Pond Improv Festival takes over the Queen City club for the second year in a row. Much like at a music festival, independent improv groups from Montréal, New York City, Boston and the Green Mountain State come together for a three-day marathon of on-the-spot hilarity. The Big Pond Improv Festival runs Thursday through Saturday, August 15 through 17, at the Vermont Comedy Club in Burlington.