In a Line Gag the players are called upon to make short quips relating to the gag type chosen by the leader. We will use the storied example of 99 strings. In 99 Strings there is a very structured format where players make gags about nouns getting kicked out of a drinking establishment.
The line of players are tasked with telling a story together. The leader will pick one player to start the story. As long as they are being pointed at (conducted) the player will continue to tell the story. Without warning the leader will switch to another player and that player will seamlessly pick up the story.
One player will step forward from the line of players and mime a door. The first player should be encouraged to create a rather mundane mime-object door. Other players must listen intently to this mime door, for they all will be required to pass through it.