vague impressions and a nasty aftertaste but little clear memory of its operational mechanics 
(ROOT (NP (NP (NP (JJ vague) (NNS impressions)) (CC and) (NP (DT a) (JJ nasty) (NN aftertaste))) (CC but) (NP (NP (JJ little) (JJ clear) (NN memory)) (PP (IN of) (NP (PRP$ its) (JJ operational) (NN mechanics))))))
(ROOT (NP (NP (NP (JJ ) (NNS )) (CC ) (NP (DT ) (JJ ) (NN ))) (CC ) (NP (NP (JJ ) (JJ ) (NN )) (PP (IN ) (NP (PRP$ ) (JJ ) (NN ))))))