( Normally ( light ( ( ( enters ( the eye ) ) ( only ( through ( ( ( the pupil ) , ) ( ( the ( dark opening ) ) ( at ( ( the center ) ( of ( the iris ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB Normally)) (NP (NN light)) (VP (VBZ enters) (NP (DT the) (NN eye)) (PP (RB only) (IN through) (NP (NP (DT the) (NN pupil)) (, ,) (NP (NP (DT the) (JJ dark) (NN opening)) (PP (IN at) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (DT the) (NNS iris))))))))) (. .)))
Normally light enters the eye only through the pupil, the dark opening at the center of the iris.
(ROOT (S (NP (DT The) (NN pupil)) (VP (VBZ is) (NP (NP (DT the) (NN name)) (PP (IN of) (NP (NP (DT the) (JJ black) (NN opening)) (PP (IN in) (NP (NP (DT the) (NN eye)) (SBAR (WHNP (WDT that)) (S (VP (VBZ lets) (SBAR (S (NP (NN light)) (VP (VBP enter))))))))))))) (. .)))