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

Example Input: Sentence1: All sharks are predators. 
Sentence2: hiding can be used for avoiding sharks.
Example Output: sharks

Example Input: Sentence1: For the heart is the chief organ of the body and rules it. 
Sentence2: Bone provides protection for the heart.
Example Output:
heart