What's Gnu

There once was a Gnu, his name was Lou.
He was a very young Gnu, who couldn't do
Everything an old Gnu knew.
At certain times, in Lou's young life, you see
He wanted to do Gnu things, like you and me,
Because, if he didn't his mood would turn blue.
That wasn't supposed to happen to he,
To become the blue Gnu, named Lou.
Lou loved to run and gambol, like a young kid
And of course, being young, that's what he did.
Playing was good for Lou the Gnu, who grew,
Into a healthy and strong, Big Lou Gnu.
As you may have already guessed or surmised,
Lou the Gnu met a girl Gnu and was surprised
To find her name was Lulu the Gnu.
They married and in a very short while,
Young Gnus arrived; Lou and Lulu did smile.