Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.
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Question: Sentence1: threatening behavior by predators causes a porcupine to extend its quills. 
Sentence2: Fishers are one of the few specialized predators on porcupines.

Answer: predators


Question: Sentence1: Oxygen fatigue is a shortage of oxygen reaching the brain. 
Sentence2: Plants can reduce fatigue during the daytime.

Answer: fatigue


Question: Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: the emission of SO2 causes acid rain.

Answer:
acid