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: Gravity is a force that pulls on things. 
Sentence2: A force that pulls on things pulls objects towards planets.
Example Output: force

Example Input: Sentence1: Polyps usually reproduce asexually. 
Sentence2: Polyps usually reproduce several different ways.
Example Output: Polyps

Example Input: Sentence1: sugar causes food to taste sweet. 
Sentence2: sugar is in fruit.
Example Output:
sugar