Poirot remained lost in thought for a few minutes. 
( Poirot ( ( remained ( lost ( in ( thought ( for ( a ( few minutes ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Poirot)) (VP (VBD remained) (VP (VBN lost) (PP (IN in) (NP (NP (NN thought)) (PP (IN for) (NP (DT a) (JJ few) (NNS minutes))))))) (. .)))
Poirot was focused deeply on his thoughts.
( Poirot ( ( was ( ( focused deeply ) ( on ( his thoughts ) ) ) ) . ) )
(ROOT (S (NP (NNP Poirot)) (VP (VBD was) (VP (VBN focused) (ADVP (RB deeply)) (PP (IN on) (NP (PRP$ his) (NNS thoughts))))) (. .)))