Sometimes the film world overlaps in ways that make my brain hurt. Take Danny Trejo — the grizzled legend of “Machete,” “Desperado,” “Spy Kids,” and countless other tough-guy roles.

His first screen appearance came in Andrei Konchalovsky’s “Runaway Train.” Trejo got onto the set thanks to Eddie Bunker, his former cellmate who later became a novelist and screenwriter. Trejo showed up as a background extra, Bunker noticed how well he boxed, and suggested he train Eric Roberts for the film.

Konchalovsky spotted Trejo as a boxing coach and offered him a small role in the movie. Trejo and Bunker would meet again years later on Michael Mann’s “Heat.”

Here’s where it gets wild: Konchalovsky studied at VGIK alongside Andrei Tarkovsky. They worked together on “Ivan’s Childhood” and “Andrei Rublev.”

So Danny Trejo and Andrei Tarkovsky are literally one handshake apart — two legends from entirely different cinematic universes.

A couple more examples

Tarkovsky watched the first “Terminator” and spoke about it with unexpected admiration (only five years separate “Stalker” and Cameron’s sci-fi debut). Michael Biehn, who played Kyle Reese, later traveled to Russia to star in Aleksei Balabanov’s “The American,” but he fell off the wagon in Norilsk, derailed production, and the film was never made.

Back to Konchalovsky. His brother Nikita Mikhalkov arrived at Cannes in 1994 with “Burnt by the Sun” as the presumed favorite — only to lose the Palme to a 30-year-old upstart from Tennessee with a complicated last name: Quentin Tarantino.

And in Tarantino’s debut “Reservoir Dogs,” who pops up in the cast? Eddie Bunker — the same guy who smuggled Trejo onto “Runaway Train.”

Everything’s connected, honestly.

P.S.

As a final twist: alongside the Weinstein brothers and Lawrence Bender, “Pulp Fiction” lists Danny DeVito as a producer.