Try this:

use strict;
use warnings;

my $a = 1;        # a simple variable
my $ref_a = \$a;  # refers to the original $a

my $a = 5;        # obscures the old $a, but
                  # ref_a still points to the old $a

print "'a' = $a; 'ref_a' points to ",  ${$ref_a}, "\n";
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Now of course you see what to expect, but in a larger program this behaviour can leave you puzzled. You should of course have created a new variable instead.