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: All life relies on a relatively narrow range of pH, or acidity. 
Sentence2: humans rely on a relatively narrow range of acidity.
Example Output: acidity

Example Input: Sentence1: Hair helps to insulate and protect the body. 
Sentence2: most mammals have insulation that also protects the body.
Example Output: body

Example Input: Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keep your food fresh, simple and as natural as possible.
Example Output:
fresh