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: Mollusks live in most terrestrial, freshwater, and marine habitats. 
Sentence2: Clams live in freshwater habitats.

Ex Output:
freshwater


Ex Input:
Sentence1: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.

Ex Output:
groups


Ex Input:
Sentence1: Optical tools Apply and distinguish between optical comparators, optical flats, and microscopes. 
Sentence2: comparators, flats, and microscopes could be used for observing materials up close.

Ex Output:

comparators