They call it aliasing, its special

#!/usr/bin/perl --
use strict;
use warnings;

my $one = "hi ";
my $two = \$one;
$_ .= "there " for $one;
$$two .= "buddy ";
$two = "bye ";
print "one=$one\ntwo=$two\n";
__END__
one=hi there buddy
two=bye
[download]

The rule sounds familiar :)