Another place that you can see it manifest is in the following script:

#!/usr/bin/perl -w -T

use strict;
print "hello ($0)\n";

#delete $ENV{$_} for qw(PATH BASH_ENV);
# may need to add more to list, PATH and BASH_ENV
# were all that drove my system crazy

exec "$1 foo"
  if ! @ARGV && $0 =~ m|^([\w\/\.]+)$|;
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Save this into a file and try to run it. It will fail until you uncomment that line. Otherwise, you could be syscalling or execing using unsecure information in the PATH and BASH_ENV variables.

my @a=qw(random brilliant braindead); print $a[rand(@a)];