( ( When ( ( the muscle ) ( moves ( forward ( -LRB- ( ( towards ( ( the ( animal 's ) ) head ) ) -RRB- ) ) ) ) ) ) ( , ( it ( ( ( ( ( ( causes ( the lungs ) ) ( to ( compress ( and ( force air ) ) ) ) ) ( out ( -LRB- ( exhale -RRB- ) ) ) ) , ) ( thus ( ridding ( ( the body ) ( of ( used air ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NN muscle)) (VP (VBZ moves) (ADVP (ADVP (RB forward)) (PRN (-LRB- -LRB-) (PP (IN towards) (NP (NP (DT the) (NN animal) (POS 's)) (NN head))) (-RRB- -RRB-)))))) (, ,) (NP (PRP it)) (VP (VBZ causes) (NP (DT the) (NNS lungs)) (PP (TO to) (NP (NNS compress) (CC and) (NN force) (NN air))) (PP (IN out) (PRN (-LRB- -LRB-) (ADJP (JJ exhale)) (-RRB- -RRB-))) (, ,) (S (ADVP (RB thus)) (VP (VBG ridding) (NP (NP (DT the) (NN body)) (PP (IN of) (NP (JJ used) (NN air))))))) (. .)))
When the muscle moves forward (towards the animal's head), it causes the lungs to compress and force air out (exhale), thus ridding the body of used air.
(ROOT (S (SBAR (IN As) (S (NP (DT a) (NN diver)) (VP (VBZ descends)))) (, ,) (NP (NP (DT the) (NN increase)) (PP (IN in) (NP (NN pressure)))) (VP (VBZ causes) (NP (NP (DT the) (NN body) (POS 's)) (NN air) (NNS pockets)) (PP (IN in) (NP (NP (DT the) (NNS ears) (CC and) (NNS lungs)) (PP (TO to) (NP (NNS compress)))))) (. .)))