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

Example Input: Sentence1: cell division often causes growth. 
Sentence2: Mitosis is cell division.
Example Output: cell

Example Input: Sentence1: Light enters the eye through an opening called the pupil. 
Sentence2: When light goes through the pupil, the iris makes it larger or smaller.
Example Output:
Light