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: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.
Example Output: pathogens

Example Input: Sentence1: if fossils of an animal or plant are found in a place then that animal or plant used to live in that place. 
Sentence2: Fossils are preserved original remains or preserved evidence of plants and animals.
Example Output: fossils

Example Input: Sentence1: Particulates are fine dust particles. 
Sentence2: smog can contain fine dust particles.
Example Output:
dust