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.

Ex Input:
Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: when a gas in an open container evaporates gas molecules slamming into one another.

Ex Output:
container


Ex Input:
Sentence1: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.

Ex Output:
harmful


Ex Input:
Sentence1: Mutations Mutations are caused by random changes in genes. 
Sentence2: random changes in genes create new genetic variation in the gene pool.

Ex Output:

changes