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: Coral Reefs Coral reefs are widely distributed in warm shallow waters. 
Sentence2: warm shallow waters provide food and shelter to many ocean organisms.
Example Output: shallow

Example Input: Sentence1: Urine leaves the body through a sphincter in the process of urination. 
Sentence2: urine leaves the body upon relaxation of a muscle.
Example Output: Urine

Example Input: Sentence1: gravity pulls objects towards planets. 
Sentence2: Gravity is a force that pulls on things.
Example Output:
gravity