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: if an animal lives under ground then that animal will be protected from a wild fire. 
Sentence2: animals that live under ground in California will be protected from some natural disasters.
Example Output: animal

Example Input: Sentence1: PALight Flashlights are the ultimate personal LED flashlights. 
Sentence2: a PALight converts chemical energy into light energy.
Example Output:
PALight