<?php

class cat {
	function say() {
		echo 'meow' . PHP_EOL;
	}
}

class dog {
	function say() {
		echo 'woof' . PHP_EOL;
	}
}

call_user_func([dog, 'say']);
call_user_func(dog . '::say');

$cat = new cat();
call_user_func([$cat, 'say']);