This is partly guesswork since I'm not at my Perl machine to test my theory at the moment, but...

in the source for Expect, http://cpansearch.perl.org/src/RGIERSIG/Expect-1.21/Expect.pm, the definition of send_slow contains this...

sub send_slow{
      ...
  while ($chunk = shift) {
    @linechars = split ('', $chunk);
    foreach $char (@linechars) {
      ...
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The while condition really should have been (defined ($chunk = shift)) in order to avoid falling out of the loop when $chunk is false. (In your case it's "0" which is false, but "" would cause the same problem.)

You could patch your copy of Expect.pm (and optionally submit the patch to the module author for good karma.)

Oc you could just patch your own code to work around it, which is the path of least resistance. According to the documentation, send_slow pauses after every individual character, not just after each string argument. So you could try changing these lines in your code

                        my @SlowChars = split(//,$_send);
                        print Dumper(@SlowChars);
                        my $return = $exp->send_slow(1,@SlowChars);
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to just

                        print Dumper($_send);
                        my $return = $exp->send_slow(1,$_send);
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Update: Remembered to add the inner parentheses to (defined ($chunk = shift)).