( ( Although ( ( most ( of ( your customers ) ) ) ( may ( think ( of ( ( the stomach ) ( as ( ( the beginning ) ( of ( the ( digestive tract ) ) ) ) ) ) ) ) ) ) ) ( , ( digestion ( actually ( ( begins ( in ( ( ( the mouth ) , ) ( where ( ( ( the action ) ( of chewing ) ) ( ( ( ( breaks up ) food ) and ) ( ( mixes it ) ( with ( ( ( ( ( a ( starch-digesting enzyme ) ) , ) amylase ) , ) ( in ( the saliva ) ) ) ) ) ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (IN Although) (S (NP (NP (JJS most)) (PP (IN of) (NP (PRP$ your) (NNS customers)))) (VP (MD may) (VP (VB think) (PP (IN of) (NP (NP (DT the) (NN stomach)) (PP (IN as) (NP (NP (DT the) (NN beginning)) (PP (IN of) (NP (DT the) (JJ digestive) (NN tract))))))))))) (, ,) (NP (NN digestion)) (ADVP (RB actually)) (VP (VBZ begins) (PP (IN in) (NP (NP (DT the) (NN mouth)) (, ,) (SBAR (WHADVP (WRB where)) (S (NP (NP (DT the) (NN action)) (PP (IN of) (NP (VBG chewing)))) (VP (VP (VBZ breaks) (PRT (RP up)) (NP (NN food))) (CC and) (VP (VBZ mixes) (NP (PRP it)) (PP (IN with) (NP (NP (NP (DT a) (JJ starch-digesting) (NN enzyme)) (, ,) (NP (NN amylase)) (, ,)) (PP (IN in) (NP (DT the) (NN saliva)))))))))))) (. .)))
Although most of your customers may think of the stomach as the beginning of the digestive tract, digestion actually begins in the mouth, where the action of chewing breaks up food and mixes it with a starch-digesting enzyme, amylase, in the saliva.
(ROOT (S (NP (NNP Digestion)) (VP (VBZ begins) (PP (IN in) (NP (DT the) (NN mouth)))) (. .)))