gistfile1.txt

#!/usr/bin/env perl

use 5.016;
use warnings;

use Try::Tiny;

try {
	die "Boom Boom";
} catch {
	given ($_) {
		when (/Boom/) {
			try {
				die "Shake shake the room"
			} catch {
				say STDERR $_;
			}
		}
	}
}

# THIS PRINTS OUT "Boom Boom"!

given introduces lexical $_ which is closed over by the anonymous subroutine passed to catch which obscures the global $_ that the catch routine populates
i.e. it does the wrong thing for horrifically complex reasons