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: Some viruses live in a dormant state inside the body. 
Sentence2: a virus can live in the brain.

Answer: viruses


Question: Sentence1: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.

Answer: erosion


Question: Sentence1: Placental mammals are therian mammals in which a placenta develops during pregnancy. 
Sentence2: humans have a placenta during pregnancy.

Answer:
placenta