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: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food at 40 degrees F or lower is used for keeping food fresh.
Example Output: food

Example Input: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: An object is an item in the real world.
Example Output: object

Example Input: Sentence1: Viruses are usually considered to be nonliving. 
Sentence2: smallpox is usually considered to be nonliving.
Example Output:
considered