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: Bacteria and Viruses Bacteria and viruses can cause diseases. 
Sentence2: bacteria can have a negative impact on an organism.
Example Output: Bacteria

Example Input: Sentence1: Nitrogen is found in proteins, nucleic acids, and chlorophyll. 
Sentence2: Life without protein is impossible.
Example Output: proteins

Example Input: Sentence1: natural disasters can cause animals to leave an environment. 
Sentence2: Life in a volcanic environment can nevertheless be treacherous for animals.
Example Output:
environment