They stab it with their silly knives
But they just can't kill the beast

The story:

I always thought that the point of those two lines was that their efforts were futile and pointless, but they kept at it anyway because they thought they were doing something productive. Those two lines were my favorite from the song because they're so profound...I was reading the lyrics on the sheet music, and when I learned those weren't the words, well, it doesn't sound as profound any more.