a frustrating ` tweener ' -- too slick 
(ROOT (NP (NP (DT a) (JJ frustrating) (`` `) (NN tweener) ('' ')) (, --) (ADJP (RB too) (JJ slick))))
(ROOT (NP (NP (DT ) (JJ ) (`` ) (NN ) ('' )) (, ) (ADJP (RB ) (JJ ))))