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: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

Answer: nest


Question: Sentence1: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.

Answer: pathogens


Question: Sentence1: Mollusks reproduce sexually. 
Sentence2: dominant invertebrate reproduce sexually.

Answer:
reproduce