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: Gravity is a force that pulls on things. 
Sentence2: A force that pulls on things pulls objects towards planets.
Example Output: force

Example Input: Sentence1: Minerals are chemical elements that are essential for body processes. 
Sentence2: minerals are needed by body processes.
Example Output: processes

Example Input: Sentence1: Bioterrorism is another potential threat in the environment. 
Sentence2: Bioterrorism is always a criminal act.
Example Output:
Bioterrorism