Unwanted escaping

Consider the following source code.

<?

if ($_SERVER['REQUEST_METHOD'] === 'POST')
{
    header ('Content-Type: text/plain');
    echo "You typed: " . $_POST['x'];
}
else
{
    echo "<form action='test.php' method='post'>
        <input type='text' name='x' value='wow' />
        <input type='submit' value='Go' />
        </form>";
}

?>

So I bring up this page, it shows me the text box and the button, and I type "That's it!" into the text box. When I click "Go", I get this:

You typed: \"That\'s it!\"

How do I stop it from producing those stupid backslashes?