constantly pulling the rug from underneath us 
(ROOT (S (ADVP (RB constantly)) (VP (VBG pulling) (NP (DT the) (NN rug)) (PP (IN from) (PP (IN underneath) (NP (PRP us)))))))
(ROOT (S (ADVP (RB )) (VP (VBG ) (NP (DT ) (NN )) (PP (IN ) (PP (IN ) (NP (PRP )))))))