( ( If ( we ( shine ( ( a light ) ( in ( their eyes ) ) ) ) ) ) ( ( their pupils ) ( ( constricts ( then ( it ( opens ( ( slowly or ) quivers ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (IN If) (S (NP (PRP we)) (VP (VBP shine) (NP (NP (DT a) (NN light)) (PP (IN in) (NP (PRP$ their) (NNS eyes))))))) (NP (PRP$ their) (NNS pupils)) (VP (VBZ constricts) (S (ADVP (RB then)) (NP (PRP it)) (VP (VBZ opens) (ADVP (RB slowly) (CC or) (RB quivers))))) (. .)))
If we shine a light in their eyes their pupils constricts then it opens slowly or quivers.
(ROOT (S (NP (DT The) (NN pupil)) (VP (VBZ is) (NP (NP (DT the) (NN opening)) (PP (IN in) (NP (NP (DT the) (NN front)) (PP (IN of) (NP (DT the) (NN eye))))))) (. .)))