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: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.

Ex Output:
egg


Ex Input:
Sentence1: Microbes are also called bacteria or microorganisms. 
Sentence2: Disease-causing bacteria have a negative impact on the body.

Ex Output:
bacteria


Ex Input:
Sentence1: a planet rotating causes cycles of day and night on that planet. 
Sentence2: Each planet has different cycles of day and night.

Ex Output:

cycles