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: Skin color is another polygenic trait. 
Sentence2: Skin color is influenced by multiple genes.

Ex Output:
Skin


Ex Input:
Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.

Ex Output:
cold


Ex Input:
Sentence1: Monotremes are mammals that reproduce by laying eggs. 
Sentence2: Platypus are monotremes.

Ex Output:

Monotremes