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: faulting of rock in Earth 's crust causes earthquakes. 
Sentence2: fault movement forms earthquakes.
Example Output: earthquakes

Example Input: Sentence1: harming an animal species causes that animal 's population to decrease. 
Sentence2: Oil spill sare harmful to animals and the enviroment.
Example Output: harming

Example Input: Sentence1: Global warming affects wildlife . 
Sentence2: it affects wildlife when worldwide temperature increases.
Example Output:
affects