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: Earthquakes are natural disasters. 
Sentence2: earthquakes can cause animals to leave an environment.
Example Output: Earthquakes

Example Input: Sentence1: Runoff water is wasted water. 
Sentence2: Streams may start with wasted water.
Example Output: wasted

Example Input: Sentence1: Most hormones are regulated by feedback mechanisms. 
Sentence2: estrogen is regulated by feedback mechanisms.
Example Output:
feedback