( This ( ( is ( called cavitation ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (VP (VBN called) (NP (NN cavitation)))) (. .)))
This is called cavitation .
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (DT the) (NN formation)) (PP (IN of) (NP (DT a) (NN water) (NN vapor) (NN pocket) (NN cavitation))))) (. .)))