The dogcow is a drawing of a rather indiscriminate-looking animal (it looks mostly like a dog but is said to have the spots of a cow) that is used in the Apple Macintosh operating system (versions before OS X) to help tell users about their printing options. You can see the dogcow (in Mac OS 9.x or earlier) by going to the Finder, looking under "Page Setup...", and then looking under printer options. The dogcow is used to show you what kind of option you've selected. For example, "Flip Horizontal" flips the dogcow to upside down.
If you click on the dogcow, the Macintosh sends you the animal's characteristic cry of "Moof"! The dogcow icon was originally created by graphic artist Susan Kare in 1987. Susan is the same artist who created the graphic interface for everyone's favorite Windows 3.1 card game, Solitaire. Microsoft has adopted its own version of the dogcow and uses it to demonstrate slide transitions in its PowerPoint application, although Apple retains its copyright on the original image and, believe it or not, the "Moof"!
In Mac OS, click on the Dogcow and you will hear "Moof"!