The Book: As the goblins feed the fires by the dwarves' trees, they sing a wicked song:
Fifteen birds in five firtrees,
their feathers were fanned in a fiery breeze!
But, funny little birds, they had no wings!
O what shall we do with the funny little things?
Roast 'em alive, or stew them in a pot;
fry them, boil them and eat them hot?
Burn, burn tree and fern!
Shrivel and scorch! A fizzling torch
To light the night for our delight,
Bake and toast 'em, fry and roast 'em!
till beards blaze, and eyes glaze;
till hair smells and skins crack,
fat melts and bones black
in cinders lie
beneath the sky!
So dwarves shall die,
and light the night for our delight,
What difference does it make? There is no significant difference to the plot, narrative, or any characterizations due to the lack of the singing.
My Opinion: As cool a song as this was, it just wouldn't have worked in film. I'm not even sure it worked in the book, to be honest. Most of Tolkein's songs make it seem like his world has this rich oral history; that all cultures and civilizations have in common a love for song. Songs like this, though, skirt the edges between "rich oral history" and "full-fledged musical." Are we, the audience, supposed to believe that the goblins have some reason to have memorized this song about a bunch of dwarves burning alive in the trees? Or did they all just spontaneously come up with the same lyrics at once? Even if it didn't stink of "sudden musical" there's something decidedly non-intimidating about carefully choreographed song, mid-battle. I'm happy this was left out.
"Alright guys, don't forget to start the chorus after the third refrain. And for Christ's sake, Gary, watch your D-sharps."