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: 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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.
Example Output: wind

Example Input: Sentence1: Whale sharks are viviparous. 
Sentence2: Whale sharks are therian mammals.
Example Output:
Whale