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: if an object in a fluid is more dense than that fluid then that object will sink in that fluid because of gravity. 
Sentence2: Most seeds are more dense than water.

Ex Output:
dense


Ex Input:
Sentence1: Populations Populations are subsets of a species. 
Sentence2: Gene flow occurs when individuals move into or out of a subset of a species.

Ex Output:
species


Ex Input:
Sentence1: Good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals. 
Sentence2: Organisms like frogspawns secrete an exoskeleton that builds up to become a reef.

Ex Output:

Frogspawn