( Snakes ( ( ( can also ) ( ( ( ( smell ( the air ) ) ( with ( their tongue ) ) ) , ) ( with ( ( the help ) ( of ( ( an ( accessory ( mouth organ ) ) ) ( -LRB- ( ( ( Jacobson 's ) organ ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Snakes)) (VP (MD can) (ADVP (RB also)) (VP (VB smell) (NP (DT the) (NN air)) (PP (IN with) (NP (PRP$ their) (NN tongue))) (, ,) (PP (IN with) (NP (NP (DT the) (NN help)) (PP (IN of) (NP (NP (DT an) (JJ accessory) (NN mouth) (NN organ)) (PRN (-LRB- -LRB-) (NP (NP (NNP Jacobson) (POS 's)) (NN organ)) (-RRB- -RRB-)))))))) (. .)))
Snakes can also smell the air with their tongue, with the help of an accessory mouth organ (Jacobson's organ).
(ROOT (S (NP (NNS Snakes)) (VP (VBP use) (NP (PRP$ their) (NN tongue)) (PP (TO to) (NP (NN smell) (NNS things)))) (. .)))
Snakes use their tongue to smell things.