The plots described so far were designed for exploring the distribution of a single variable and the relationship among two variables. This section describes some plots and techniques that are useful for exploring the relationship among three or more variables. The techniques and plots described in the first four subsections are simple, requiring only simple commands to the listener and mouse actions. The fifth subsection introduces the concept of a plot object and the idea of sending messages to an object from the listener window. These ideas are used to add lines and curves to scatter plots, and the basic concepts of objects and messages will be used again in the next section on regression models. The final subsection shows how Lisp iteration can be used to construct a dynamic simulation -- a plot movie.