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: Echinoderms use pheromones to communicate with each other. 
Sentence2: Echinoderms are known for their round symmetry.

A: Echinoderms
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Q: Sentence1: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.

A: sifter
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Q: Sentence1: high temperatures can cause an object to combust. 
Sentence2: being near the sun can cause an object to combust.

A:
cause
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