when it is n't incomprehensible 
(ROOT (SBAR (ADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ is) (RB n't) (ADJP (JJ incomprehensible))))))
(ROOT (SBAR (ADVP (WRB )) (S (NP (PRP )) (VP (VBZ ) (RB ) (ADJP (JJ ))))))