by a natural sense for what works 
(ROOT (PP (IN by) (NP (NP (DT a) (JJ natural) (NN sense)) (PP (IN for) (SBAR (WHNP (WP what)) (S (VP (VBZ works))))))))
(ROOT (PP (IN ) (NP (NP (DT ) (JJ ) (NN )) (PP (IN ) (SBAR (WHNP (WP )) (S (VP (VBZ ))))))))