We all use ping all of the time to check to see if a network node is up and running (at least us techy-geeks do anyhow). Until today I did not realize that ping is in fact a duck:

Ping! I love that duck!

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Updated 2021 : note that the above post was originally published in 2007, and is left here for archival purposes. The linked review is still online, and is still the greatest Amazon review ever written (fact).