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: Autumn brings the changing of the seasons. 
Sentence2: Earth 's tilt on its rotating axis causes autumn.
Example Output: Autumn

Example Input: Sentence1: Instead, the body is covered with a protective shell of bony armor. 
Sentence2: Most mollusks have protective of bony armor.
Example Output: armor

Example Input: Sentence1: a mold spore has a negative impact on the respiratory system. 
Sentence2: water-damaged carpets have a negative impact on the respiratory system.
Example Output:
impact