To be human is to keep rattling the bars of the cage of existence, hollering, 'What's it for?'

a prisoner in a cage. He has a cup he is rattling against the bars, but he is still in his cage.

To be human is to keep rattling the bars of the cage of existence hollering, ''What's it for?''

I talk about very serious human affairs but with a lightness of heart.

The wild, cruel beast is not behind the bars of the cage. He is in front of it.

Stone walls do not a prison make, nor iron bars a cage.