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: gills are used for breathing water by aquatic animals. 
Sentence2: gills are used for breathing water by sharks.

Ex Output:
are


Ex 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.

Ex Output:
gas


Ex Input:
Sentence1: cell division often causes growth. 
Sentence2: Tumor simply means abnormal growth.

Ex Output:

growth