crawls along at a snail 's pace 
(ROOT (S (VP (VBZ crawls) (ADVP (RP along)) (PP (IN at) (NP (NP (DT a) (NN snail) (POS 's)) (NN pace))))))
(ROOT (S (VP (VBZ ) (ADVP (RP )) (PP (IN ) (NP (NP (DT ) (NN ) (POS )) (NN ))))))