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: sharpening an object causes that object to change shape. 
Sentence2: sharpening a knife causes it to change shape.
Example Output: causes

Example Input: Sentence1: Producers use energy and inorganic molecules to make food. 
Sentence2: Green plants use energy and inorganic molecules to make food.
Example Output: energy

Example Input: Sentence1: refracting sunlight causes sunlight to split into different colors. 
Sentence2: Light splits into different colors when sunlight hits raindrops.
Example Output:
colors