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: the ovaries are used in reproduction. 
Sentence2: Egg released by the ovary.
Example Output: ovaries

Example Input: Sentence1: Telephone Telephone calls are expensive. 
Sentence2: Communicating by transmitting sound is expensive.
Example Output: expensive

Example Input: Sentence1: Some viruses have an envelope of phospholipids and proteins. 
Sentence2: Phospholipases are the enzymes that degrade phospholipids .
Example Output:
phospholipids