Shouldn't
foreach(split(//,$response)) {
be
foreach(split(//,$response->content)) {

if (!$response->is_success) { should be before the loop, not in it.

What follows is the above fixes, in addition to unpacking two bytes at a time instead of one:

if (!$response->is_success) {
   die $response->status_line;
}

my $content = $response->content();

$content =~ s/^(..)//;
# One of these, depending on byte ordering of the source.
my $index = unpack('n', $1);
#my $index = unpack('v', $1);
printf("index: %04x\n", $index);

while ($content =~ /(..)/g)) {
   # One of these, depending on byte ordering of the source.
   my $int16 = unpack('n', $1);
   #my $int16 = unpack('v', $1);
   $int16 -= 65536 if ($val > 32767);
   print($int, ' ');
}
print "\n";
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Update: I wasn't converting them to signed numbers.