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.

Example Input: Sentence1: if an object is kicked then force is exerted on that object. 
Sentence2: if an object is kicked then a measurement of newtons is exerted on that object.
Example Output: exerted

Example Input: Sentence1: moss causes chemical weathering. 
Sentence2: Sphagnum moss mixed with peat moss.
Example Output: moss

Example Input: Sentence1: if gas is heated then that gas will expand. 
Sentence2: if nitrogen is heated it will expand.
Example Output:
expand