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.
--------
Question: Sentence1: Mammals generate heat mainly by keeping their metabolic rate high. 
Sentence2: food keeps mammals' metabolic rates high.

Answer: Mammals


Question: Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

Answer: nest


Question: Sentence1: Thyroid hormones increase the rate of metabolism in cells throughout the body. 
Sentence2: Cell metabolism is a heat production.

Answer:
metabolism