When they reach the end of the verse they stop, the single in the middle performs an action (such as Highland dancing), which everyone then imitates, before starting the verse again, often changing the single player to a boy, or a boy can join the center player - thus creating an extra verse in the song ("Did you ever see a laddie...").
When they reach the end of a verse, a single performer performs an action (like Highland dancing), which everyone else imitates. Then, they start the verse again, often switching the lead singer to a boy or a boy joining the center player, creating an extra verse in the song ("Did you ever see a laddie...").