Or do, :P

sub split_it_this_a_way {
    my $string = shift || die "die, die, kill you all!";
    my ( $second, $first ) = split '\.', reverse($string), 2;
    ( ~~reverse($first), $second );
}

my $str = "x.z.y";
print $str, " -> ", join(" + ", split_it_this_a_way($str)), $/;
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...because that's, uh, easier... uh, to, uh...