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: Bees feed on nectar and pollen. 
Sentence2: Plant reproduction often requires bees and nectar.

Ex Output:
Bees


Ex Input:
Sentence1: Mutations are essential for evolution to occur. 
Sentence2: Genes are altered for evolution to occur.

Ex Output:
evolution


Ex Input:
Sentence1: Amphibians have sense organs to smell and taste chemicals. 
Sentence2: Bullfrogs can smell and taste chemicals through sense organs.

Ex Output:

chemicals