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: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
Example Output: groups

Example Input: Sentence1: Lancelet larvae are free-swimming. 
Sentence2: some larvae lack a hardened backbone.
Example Output: larvae

Example Input: Sentence1: Some viruses live in a dormant state inside the body. 
Sentence2: True influenza is caused by one of the influenza viruses.
Example Output:
viruses