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

Example Input: Sentence1: Lymph is a fluid that leaks out of capillaries into spaces between cells. 
Sentence2: Humans are made up of trillions of cells.
Example Output: cells

Example Input: Sentence1: pollination requires pollinators. 
Sentence2: Several plant species require flooding for seeding establishment.
Example Output:
requires