The website
http://www.elyrics.net/read/k/killers-lyrics/human-lyrics.html

gives this stanza:

Are we human or are we dancers?
My sign is vital, my hands are cold
And I'm on my knees looking for the answer
Are we human or are we dancers?

Since the rhyming word is 'answer', the word 'dancers' must be right.
'Denser' would be unlikely by both rhyme and grammar.

As for the deeper meaning, that's a harder question.  I'd guess something like:

Are we fully human, or are we only mechanical dancing machines?

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