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: Cows are social animals. 
Sentence2: when a cow moves, chemical energy is converted to mechanical energy.
Example Output: Cows

Example Input: Sentence1: Veins generally carry deoxygenated blood. 
Sentence2: Blood carries blood cells.
Example Output: blood

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