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: when electricity flows to a light bulb , the light bulb will turn on. 
Sentence2: water pumps can turn on light bulbs.
Example Output: bulb

Example Input: Sentence1: camouflage is used for protection by prey against predators. 
Sentence2: blending is used for protection.
Example Output: protection

Example Input: Sentence1: Metamorphic Rocks Metamorphic Rocks Metamorphic rocks are formed by pressure and heat. 
Sentence2: extreme heat and pressure form a type of rock.
Example Output:
formed