scratch for a lesson in scratching 
(ROOT (NP (NP (NN scratch)) (PP (IN for) (NP (NP (DT a) (NN lesson)) (PP (IN in) (NP (NN scratching)))))))
(ROOT (NP (NP (NN )) (PP (IN ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NN )))))))