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: Generally, pheromones are volatile substances. 
Sentence2: Male dogs use volatile substances in urine to mark their territory.
Example Output: substances

Example Input: Sentence1: All photos are digital images. 
Sentence2: satellites are used to take photos from space.
Example Output: photos

Example Input: Sentence1: volcanic ash in the atmosphere decreases the temperature by blocking the sun. 
Sentence2: Eruptive products of Hawaiian volcanoes span a wide range of temperatures.
Example Output:
temperature