Definition: 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.
Input: Sentence1: Ethologists usually study how animals behave in their natural environment. 
Sentence2: Ethologists usually study how animals use instincts in their natural environment.

Ethologists