( This ( ( is ( due ( to ( ( the ( smooth ( muscle contractions ) ) ) ( in ( ( the ( female ( reproductive organs ) ) ) ( caused ( by ( ( the nerve-stimulus ) ( of mating ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (ADJP (JJ due) (PP (TO to) (NP (NP (DT the) (JJ smooth) (NN muscle) (NNS contractions)) (PP (IN in) (NP (NP (DT the) (JJ female) (JJ reproductive) (NNS organs)) (VP (VBN caused) (PP (IN by) (NP (NP (DT the) (NNS nerve-stimulus)) (PP (IN of) (NP (NN mating)))))))))))) (. .)))
This is due to the smooth muscle contractions in the female reproductive organs caused by the nerve-stimulus of mating.
(ROOT (S (NP (NNS Muscles)) (VP (VBP need) (NP (NN stimulus)) (PP (TO to) (NP (NN contract)))) (. .)))