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: Parasites are organisms that live off a host. 
Sentence2: roundworms may be free-living or live off a host.
Example Output: host

Example Input: Sentence1: Male dogs use pheromones in urine to mark their territory. 
Sentence2: Pheromones are hormones that are thought to stimulate, through smell, sexual reactions in animals.
Example Output: pheromones

Example Input: Sentence1: Chloroplasts Chloroplasts serve as the site of photosynthesis. 
Sentence2: The site of photosynthesis in plant and algae cells is found within organelles.
Example Output:
photosynthesis