"Song pluggers" were pianists and singers who represented the music publishers, making their living demonstrating songs to promote sales of sheet music. Most music stores had song pluggers on staff. Other pluggers were employed by the publishers to travel and familiarize the public with their new publications. Among the ranks of song pluggers were George Gershwin, Harry Warren, Vincent Youmans and Al Sherman. A more aggressive form of song plugging was known as "booming": it meant buying dozens of tickets for shows, infiltrating the audience and then singing the song to be plugged. At Shapiro Bernstein, Louis Bernstein recalled taking his plugging crew to cycle races at Madison Square Garden: "They had 20,000 people there, we had a pianist and a singer with a large horn. We'd sing a song to them thirty times a night. They'd cheer and yell, and we kept pounding away at them. When people walked out, they'd be singing the song. They couldn't help it."