(S (S (S (NP (BASENP (NNS Incidents)) (PP (IN like) (BASENP (DT this)))) (VP (VBP have) (VP (VBN happened) (ADVP (RB before))))) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (BASENP (NNS researchers)) (VP (VBP have) (VP (VP (VBN tracked) (BASENP (DT the) (NN cause))) (ADVP (RB down) (PP (TO to) (NP (BASENP (DT the) (NN fish)) (VP (VBG eating) (BASENP (JJ poisonous) (NN seaweed))))))))))) (PERIOD .))