See Moof. The dogcow is a semi-legendary
creature that lurks in the depths of the Macintosh Technical Notes
Hypercard stack V3.1. The full story of the dogcow is told in technical
note #31 (the particular dogcow illustrated is properly named
‘Clarus’). Option-shift-click will cause it to emit a
characteristic Moof!
or !fooM
sound.
Getting to tech note 31 is the hard part; to discover
how to do that, one must needs examine the stack script with a hackerly
eye. Clue: rot13 is involved. A dogcow also
appears if you choose ‘Page Setup...’ with a LaserWriter
selected and click on the ‘Options’ button. It also lurks in
other Mac printer drivers, notably those for the now-discontinued Style
Writers. See http://developer.apple.com/products/techsupport/dogcow/tn31.html.