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: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.
Example Output: cold

Example Input: Sentence1: infection can cause bodily tissues to swell. 
Sentence2: Bacteria can cause bodily tissues to swell.
Example Output: bodily

Example Input: Sentence1: animals require water for survival. 
Sentence2: Drought can negatively impact animal survival.
Example Output:
animals