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: a pulley is used for lifting objects. 
Sentence2: Resistance exercises are weight-lifting exercises.
Example Output: lifting

Example Input: Sentence1: sonar is used to find the location of an object. 
Sentence2: Surface ships use sonar to locate and track submarines.
Example Output: location

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