only the most practiced curmudgeon could fail to crack a smile at 
(ROOT (S (NP (RB only) (DT the) (ADJP (RBS most) (VBN practiced)) (NN curmudgeon)) (VP (MD could) (VP (VB fail) (S (VP (TO to) (VP (VB crack) (NP (DT a) (NN smile)) (PP (IN at)))))))))
(ROOT (S (NP (RB ) (DT ) (ADJP (RBS ) (VBN )) (NN )) (VP (MD ) (VP (VB ) (S (VP (TO ) (VP (VB ) (NP (DT ) (NN )) (PP (IN )))))))))