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: a light bulb is used for seeing in the dark. 
Sentence2: Conventional light bulbs generate light by heating a filament.
Example Output: bulb

Example Input: Sentence1: Finally, the fluid in the nephron reaches a collecting duct . 
Sentence2: fluid in the kidneys collect into ducts.
Example Output: fluid

Example Input: Sentence1: a rubber band snapping causes the particles in the rubber band to vibrate. 
Sentence2: Sound waves are vibrations in matter.
Example Output:
vibrate