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: All frogs are amphibians.
Sentence2: frogs have permeable skin that easily absorbs substances from the environment.

Answer: frogs

Question: Sentence1: the uterus is used in reproduction.
Sentence2: Reproduction uses the same organ as menstruation.

Answer: reproduction

Question: Sentence1: Playing is just one of many ways that mammals and other animals learn how to behave.
Sentence2: Animals learn to behave to increase chances of survival.

Answer:
animals