These are particularly tricky when short words, like articles or pronouns, are 
( These ( are ( particularly ( tricky ( when ( ( short words ) ( , ( ( like ( ( articles or ) pronouns ) ) ( , are ) ) ) ) ) ) ) ) )
(ROOT (S (NP (DT These)) (VP (VBP are) (ADJP (RB particularly) (JJ tricky) (SBAR (WHADVP (WRB when)) (S (NP (JJ short) (NNS words)) (, ,) (PP (IN like) (NP (NNS articles) (CC or) (NNS pronouns))) (, ,) (VP (VBP are))))))))
Articles and pronouns make these tricky.  
( ( ( Articles and ) pronouns ) ( ( make ( these tricky ) ) . ) )
(ROOT (S (NP (NNS Articles) (CC and) (NNS pronouns)) (VP (VBP make) (S (NP (DT these)) (ADJP (JJ tricky)))) (. .)))