When a Dock item jumps up and down
At some point you might see a Dock item jumping up and down, over and over, as if it's trying to get your attention. It is. This means that particular application needs you—click on the jumping icon and that application will “come forward.” Then you will probably see a message on the screen that needs to be taken care of, such as “Do you want to save this document” or “This application couldn't do what you wanted.” Just do what it wants you to do.
This is different from the “bouncing” you will see when an icon starts to open (as you'll see in Chapter 6). The bounce is little; the jump is big. It's actually kind of cute.