( ( Watch ( for ( ( bubbles or ) gas ) ) ) ( ( displacing ( ( the water ) ( in ( the tube ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Watch)) (PP (IN for) (NP (NNS bubbles) (CC or) (NN gas)))) (VP (VBZ displacing) (NP (NP (DT the) (NN water)) (PP (IN in) (NP (DT the) (NN tube))))) (. .)))
Watch for bubbles or gas displacing the water in the tube.
(ROOT (S (NP (NNP Gas) (NN bubble) (NNS holes)) (VP (VBZ helps) (NP (NP (JJ pumice) (NN float)) (PP (IN in) (NP (NN water))))) (. .)))