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.

Example Input: Sentence1: Pregnancy is the carrying of one or more offspring from fertilization until birth. 
Sentence2: An elephant carries their offspring from fertilization until birth, 22 months later.
Example Output: fertilization

Example Input: Sentence1: Most people know that the Venus Flytrap is a carnivorous plant. 
Sentence2: The Venus Flytrap has specialized reproductive organs.
Example Output: Flytrap

Example Input: Sentence1: high mountains with well-rounded peaks can be formed by collision of crustal plates. 
Sentence2: earthquakes can result in formation of high mountains with well-rounded peaks.
Example Output:
formed