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: an animal requires nutrients to grow and heal. 
Sentence2: Microbes can help an animal to grow and heal.
Example Output: grow

Example Input: Sentence1: Oil and gasoline are fossil fuels. 
Sentence2: lawn mowers convert fossil fuels into motion.
Example Output: fossil

Example Input: Sentence1: plasma is formed by electrons separating from atoms in stars. 
Sentence2: Stars shine because they are hot .
Example Output:
stars