Looking through old notebooks, I found a poem about the same metaphor, but with a different energy entirely. It's older, so obviously not my best work, but still a pleasant surprise I'd like to share.
Iron bars and burlap sacks,
thats what he described me as.
just metal and skin,
with a brain added in,
stoic, heroic, immune to the pin.
but the pin was a word and the word was a knife,
and the thick leather tore, letting loose all the lies.
what broke free and flew out
was just sorrow and clouds,
and a bright bleeding heart, full of frightening sounds.
a burlap sack of iron bars;
to the rest of the world, that's who we are.
just metal and leather,
never under the weather.
but deep down lies the heart, encircled in feathers.