Characters
Old McDonald had a farm. Eee-Eye-Eee-Eye Oh. And on that farm he shot some guys. Eee-Eye-Eee-Eye-Oh!
— McManis · The Usual Suspects

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker twists the children's farm song into something grim, keeping the cheerful refrain but replacing the animals with a boast that people were shot there. The bouncy chant set against violence gives the line a darkly mocking, sing-song menace.
Context reviewed