true, most probably cause of it's magic behavior as handle-method. Though looking into IO::Handle might help.

Anyway, I don't know what your prints are supposed to do, but before relying on source-filtering I'd rather rename them like dbout or out or say.

The following code breaks on each output, simply uncommenting use feature disables this behavior.

#use feature 'say';

sub say {
  print @_,"\n";
  no warnings 'once';
  $DB::single=1;
}

say $x++;
say $x++;
say $x++;
say $x++;
say $x++;
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> ps. thanks for the link to obsidianrook, I always enjoy those presentations!

Well, better thank doom directly! =)