Explanation:

A Touch Sensor is a leaf node in VRML 2.0 which receives special events from the browser whenever the mouse cursor affects its siblings. These events can be one of the following two:

• The mouse cursor has just touched the object(s), or
• The user has clicked on the object(s).

The Touch Sensor is used whenever you want to grab this type of input from the user. Its actual use is not dictated here, but below (and in the Java program), but to form the infrastructure for its use all you need to add is this one line. In this example, the Touch Sensor is affecting the Shape node immediately following it (remember, Touch Sensors affect all of their siblings!).