In stead of:

my @chars = split( //, $in );
foreach my $char (@chars) {
   $check += ord($char);
}
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You could use:

$check += ord $_ for split //, $in;
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But to your question, I don't know. I think I read an explanation once by Dominus, on the mailing list to his superb book Higher Order Perl (which I highly recomend!)

Edit: In light of BrowserUk's response below, it's unlikely that this is related to the explanation I mentioned above. Sorry for confusing...