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: Sweat glands produce more sweat. 
Sentence2: When the body is hot, something coming from a gland is produced to cool the body.
Example Output: glands

Example Input: Sentence1: Evolution is a change in the characteristics of living things over time. 
Sentence2: An organism is a living thing.
Example Output:
living