[PHP] Why $_REQUEST do the same thing as mysql_escape_string()

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I put some thing in an form input filed like this:
' " \
then submit to a php script.
When use $_GET / $_POST / $_REQUEST to get the value,
I always get:
\' \" \\
In php expression it should be:
$_REQUEST['field'] = "\\' \\\" \\\\";

Any one who can tell me why?