for my $offset ( 0 .. $#ary_a ) {
    foobar( $ary_a[ -$offset ], $ary_b[ -$offset ] );
}

##</code><code>##

for my $offset (1..@ary_a) {
    foobar( $ary_a[ -$offset ], $ary_b[ -$offset ] );
}