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: the Earth being tilted on its rotating axis causes seasons. 
Sentence2: the planet's orbit and tilt causes seasons.
Example Output: seasons

Example Input: Sentence1: All lizards are reptiles. 
Sentence2: Lizards are tetrapod vertebrates that produce amniotic eggs.
Example Output: lizards

Example Input: Sentence1: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: Phases refer to the different shapes the moon appears from the earth.
Example Output:
moon