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: Centrioles come in pairs. 
Sentence2: Something that comes in pairs are organelles involved in cell division.

Ex Output:
come


Ex Input:
Sentence1: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.

Ex Output:
snail


Ex Input:
Sentence1: Bird eggs have hard, calcium carbonate shells. 
Sentence2: All hawks are birds.

Ex Output:

Bird