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: Competition may lead to aggressive behaviors or displays of aggression. 
Sentence2: Aggression Aggression and violence often go together.
Example Output: aggression

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: Passive immunity lasts only as long as the antibodies survive in body fluids. 
Sentence2: passive immunity lasts only as long as the antibodies survive in blood.
Example Output:
Passive