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: Electrical currents cause magnetic fields. 
Sentence2: Electrical currents can cause objects to repel each other.
Example Output: Electrical

Example Input: Sentence1: forming coal requires decaying vegetation. 
Sentence2: Forming fossil fuels requires decaying vegetation.
Example Output: decaying

Example Input: Sentence1: a plant requires food for survival. 
Sentence2: A plant requires leaves for survival.
Example Output:
a