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: forming coal requires decaying vegetation. 
Sentence2: Forming fossil fuels requires decaying vegetation.
Example Output: decaying

Example Input: Sentence1: Rain is good, but lots of rain causes destructive flooding. 
Sentence2: Stormy weather increases the chances of flooding.
Example Output:
flooding