It can break bad exactly because of scope. The variables declared in the outer sub are not properly shared to the inner subs (or rather, they are shared only in the first run).

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

sub outer {
    my ($x) = @_;

    sub inner {
        return $x + 1
    }
    return inner()
}

print outer(12), "\n";  # 13
print outer(42), "\n";  # 13 !!
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Also, you'll get a warning:

Variable "$x" will not stay shared at 1.pl line 9.
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