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: Light source is an ultra-bright, unbreakable LED Bulb. 
Sentence2: LEDs convert electricity into light and heat energy.
Example Output: LED

Example Input: Sentence1: hitting an object causes the particles in that object to vibrate. 
Sentence2: Frequency is the measurable rate of that vibration.
Example Output:
vibrate