为什么我print_r($_REQUEST); 获取到的值有哪个 guid 就是这个样子

为什么我print_r($_REQUEST);  获取到的值有哪个  guid   就是这个样子

$_POST 
Array ( [keywrods] => ccccc )
$_REQUEST 
Array ( [keywrods] => ccccc [__guid] => 193203115.2666915292876795400.1513761710173.5144 [UM_distinctid] => 16073412bcd26b-082849260aa57a-5d4e211f-1fa400-16073412bcf3ac [PHPSESSID] => 0v1lodu4ccf0r69j2nmf16sqo6 [CNZZDATA1253472858] => 839258152-1513761246-http%3A%2F%2Fwww.gr.com%2F|1513835835 [monitor_count] => 53 )