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: Erosion of rock makes nutrients available. 
Sentence2: rain causes nutrients to be available.
Example Output: nutrients

Example Input: Sentence1: harming an animal species has a negative impact on the population size of that species. 
Sentence2: the rarity of a species increases harm to population exponentially.
Example Output: harming

Example Input: Sentence1: Telescopes have detected planets orbiting nearby stars. 
Sentence2: Astronomers use telescopes to detect planets.
Example Output:
detected