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.

Input: Consider Input: Sentence1: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.

Output: egg


Input: Consider Input: Sentence1: Carbon cycles quickly between organisms and the atmosphere. 
Sentence2: the atmosphere is essential to all living organisms.

Output: organisms


Input: Consider Input: Sentence1: Reptiles are a class of tetrapod vertebrates that produce amniotic eggs. 
Sentence2: birds have amniotic eggs.


Output: eggs