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: Every photograph is produced by a camera. 
Sentence2: Photographers record images.
Example Output: photograph

Example Input: Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: If you place gas in an open box it will evaporate and spread out into the air.
Example Output: gas

Example Input: Sentence1: Sperm are deposited in the vagina during sexual intercourse. 
Sentence2: Several hundred million sperms are released during sexual intercourse.
Example Output:
intercourse