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 frogs are amphibians. 
Sentence2: frogs have permeable skin that easily absorbs substances from the environment.
Example Output: frogs

Example Input: Sentence1: the mass of an object causes the gravitational force exerted by that object. 
Sentence2: gravitational force accelerates objects.
Example Output: force

Example Input: Sentence1: Cancer genes can be inherited. 
Sentence2: Cancer genes can be genetic.
Example Output:
Cancer