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 organism can gain energy by assimilation or absorption of food. 
Sentence2: Organisms require food for growth.

A: food
****
Q: Sentence1: poisonous darts are used for defense by sea anemones. 
Sentence2: poisonous darts are used for protection by sea anemones.

A: anemones
****
Q: Sentence1: Ethologists usually study how animals behave in their natural environment. 
Sentence2: Environments reflect native habitats.

A:
environment
****