Earlier today someone in IRC chat room pointed out me an easter egg (hidden feature or message in a game or software or sound track) for Ubuntu Linux.

apt-get command easter egg

Open your terminal and type the command:

apt-get moo

         (__)
         (oo)
   /------\/
  / |    ||
 *  /\---/\
    ~~   ~~
...."Have you mooed today?"...

aptitude command easter egg

Also try out following at a shell prompt:
aptitude -v moo
Output:

There really are no Easter Eggs in this program.

Now try one more time:
aptitude -vv moo
Output:

Didn't I already tell you that there are no Easter Eggs in this program?

Heh, keep adding more v options to a command:
aptitude -vvv moo
aptitude -vvvvv moo

I’m sure there are more easter eggs. I’d love to read about more hidden features in the comments section below.