Suck and rust the oxygen in gulps
And spit the metal directly back up the barrel
In colloquial usage, the term “rust” means red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture.
Bullets, referred to in the last line, are made of lead or iron.
Aesop literally bites the bullet — an idiom usually used to mean enduring a painful situation that is unavoidable — which would create a combination of iron and oxygen (his breath — “in gulps”), thus generating rust.
He then spits the bullet directly back up the barrel, implying in the metaphorical sense that any bad shit that comes his way he will chew up and spit back right where it came from.
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