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.

Q: Sentence1: cell division often causes growth. 
Sentence2: Mitosis is cell division.

A: cell
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Q: Sentence1: Some pelycosaurs gave rise to a group of animals called therapsids. 
Sentence2: Like most other groups of synapsids, all pelycosaurs are now extinct.

A: pelycosaurs
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Q: Sentence1: Playing is one way mammals and other animals learn how to behave. 
Sentence2: Playing is one way cats learn how to behave.

A:
Playing
****