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: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: cars transform chemical energy into mechanical energy.

A: chemical
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Q: Sentence1: harming an animal species causes that animal 's population to decrease. 
Sentence2: Wild animal populations have decreased drastically, due to both hunting and loss of habitat.

A: animal
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Q: Sentence1: thirst is used to make an animal realize that it needs to replenish its bodily water by the body. 
Sentence2: Animals need to replenish water to avoid dehydration.

A:
animal
****