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: Light is the visible form of electromagnetic energy. 
Sentence2: Electromagnetic energy enters the eye through an opening called the pupil.
Example Output: electromagnetic

Example Input: Sentence1: With a spatula, fold in flour mixture. 
Sentence2: a sifter is used for separating flour.
Example Output: flour

Example Input: Sentence1: Mitosis is a simple, single cell division . 
Sentence2: Mitosis often causes growth.
Example Output:
Mitosis