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: Mammalian predators include the coyote and bobcat. 
Sentence2: a coyote's teeth is important for digestion.
Example Output: coyote

Example Input: Sentence1: forming coal requires decaying vegetation. 
Sentence2: Forming fossil fuels requires decaying vegetation.
Example Output: decaying

Example Input: Sentence1: friction causes an object to lose energy. 
Sentence2: Friction occurs when surfaces rub together.
Example Output:
friction