$stack = array();
    foreach($big as $add){
        $last = $add[count($add)-1];
        array_push($stack, "hey");
    }
    echo '<pre>';
    print_r($arr);
    echo '</pre>';

/* PRODUCES */

Array
(
    [0] => hey
)
Array
(
    [0] => hey
)
Array
(
    [0] => hey
)
Array
(
    [0] => hey
)